Some say manifold vacuum...some say ported. As far as we're concerned, there's only one right way to power your distributors vacuum advance. Here's a quick demonstration that shows why.
I read an article by one of the engineers involved with designing these systems, he knows what he is talking about and says you always want to use full manifold vacuum. It keeps your engine cooler at idle due to the added advance, and has other benefits as well. Ported was something that was used later on to attempt to help emissions.
I have not run across an engine yet that performs better with ported vacuum than manifold vacuum. Ported was an emissions era crutch from the early 70s. All the 60s engines used manifold vacuum.
my 1987 Honda CRX came from the factory as manifold vacuum. Had many people tell me to change it to ported instead of manifold. Pretty much ran the same at cruise, but at idle it was terrible, and would start overheating because of how hot the headers were getting on ported vacuum (about 5 or so degrees of timing (no vac, no mech) ), manifold vac would put it at around 20 degrees of timing (vac timing, no mech) and idles incredibly smooth
Switching to manifold vacuum cured almost all my problems. New rebuilt 350 stock except for an RV cam. New holley 600. new MSD distributor the list goes on and on.. Never could get it to idle correctly no matter what I did. 14 degrees btdc. Finally read that article, switched to manifold vacuum and its like a new car. It runs and drives so much better its unbelievable.
Yeah, uncle tony is wrong on this one. Listen to the actual automotive engineers describe the purpose of manifold vacuum advance. Tony has it backwards
@@theungoliant9410 I’m sorry I don’t have one. You’ll have to run a search on the subject. I’m sure it won’t take long to find - it didn’t for me when I dug into the subject. There were two engineers in particular who have written extensively on the subject. If I remember correctly, one of them was a former GM engineer. Very interesting information
Same thing ... I switched to manifold and it's suddenly running so much better, it's unbelievable. Idles perfect, and you you tap the throttle, it just wants to go. For 40 years I've always done manifold from American Chevy 350s, Ford 289s, most European cars. Today many advice ported so I've been having a go at that. Nope. just doesn't work for a normal daily driver car with traffic choked roads in my hot tropical country.
Vacuum Advance plays a huge part in Fuel mileage... I have found on my tunnel ram setup I get better driveability from Manifold vacuum.. you can use adjustable vacuum pots so you can dial in your vacuum advance and have your cake and eat it too....
I just made the switch to manifold on my 72 f350. Of course I had to make plenty of adjustments with timing but it was far superior to ported. The first thing I noticed was how quiet it was on a cold start. The engine ran much better and my mpgs went up by 3. I just don’t get why you’d want to run ported
One thing Tony doesn’t mention is, retarding timing under throttle can prevent detonation which can be a good thing in a performance engine. I run manifold vacuum and got a smoother idle and it stopped pinging at WOT.
I get that too, far superior performance and driveability on manifold vacuum. This debate will continue on, at the end to each his own. I'm happy always with manifold vacuum.
Absolutely correct. The biggest problem is that the off-the-shelf distributors have too much mechanical advance for ported vacuum. I had DUI build me a distributor with 12 degrees mechanical advance and a 14 degree vacuum canister. I start with 24 degrees initial timing which using ported vacuum is your idle timing. But I vary that from about 22-26 degrees as needed. So this gives me 24 degrees at idle, 36 degrees total timing and 50 degrees light load cruise which is exactly what a first generation SBC wants. My engines all run perfect. For Ported Vacuum Idle 24 > 12 mechanical advance Total 36 > 14 vacuum advance Cruise 50
DUI recommends manifold in their literature. How many of those 14 degrees ported vacuum advance are you getting at high speed/low load cruise? At low load, manifold vacuum is high and ported is quite low obviously. Run two gauges at once to validate. Seems like you could be getting more mpgs out of your cruise with more timing, manifold timing.
it’s all the same except at idle and WOT (wot has no vacuum anyways so it’s a moot point). Manifold has higher timing advance at idle, lower EGT’s and not as good emissions, then pulls timing as the throttle blades are opened. Ported vacuum has no advance at idle, because it sees no vacuum at idle. As the throttle blades are opened, the vacuum rises and it adds timing advance. The way that you determine which is best is the way your distributor curve is set up, and your application. Some guys will swear by ported only, others by manifold only. If you have the ability to use a dyno I’m sure there’s a negligible difference in part throttle power, because in the middle of the part throttle operation, with the manifold vacuum advance dropping and the ported rising, they intersect at the same amount of advance. So, to sum it up, they achieve the same effect, just one adding timing and one taking timing out. The engine will run differently on each due to the way they add or remove timing. Remember, this is only idle and vacuum cruising, wide open throttle doesn’t matter for vacuum advance.
6 of one half a dozen of the other.Your description is pretty spot on i think. I remember having a '71 ford fe that had a coolant temp vacuum switch that when coolant temp got to a determined level it would route manifold vacuum to the dist. in order to increase timing and raise idle speed.That car detonated like mad on any kind of a part throttle load and started my education of vacuum advance. I remember trying so hard to keep the vacuum advance and tune out the detonation cause why I don't know.... because i was giving up maybe a mpg in fuel economy i guess LoL
I thought the only difference between full vac and ported was having extra advance at idle. Ported timing waits until throttle is just off idle to work. So it makes no difference either way. The power and fuel economy is the same. The only change from the exta timing at idle is smoother idle, cooler temp, better vacuum assist to power brakes, ect. depending on your engine combo, it may run better at idle. The higher vacuum signal lets you lower the throttle plates even more to gain better results from your idle mixture screws. Remember, we always set our base timing and and check max timing with the vacuum advance disconnected anyway. WOT doesn't use vacuum advance, so there should never be a change in performance. Anyone who disagrees must be setting their base timing with vacuum advance connected. This is wrong and will affect many things negatively. Love your videos, Tony!
Ported vacuum is pretty low just off idle and manifold vacuum is pretty high just off idle. You’re getting much more advance with manifold in that situation. It’s not just idle where the difference is. In fact, most vacuum canisters I’ve come across don’t start advancing timing until about 5 hg. So if your canister is connected to ported and you’re in light cruise with those throttle blades barely cracked, you’d be getting zero advance. If you were connected to manifold you’d be getting all of it - like you should.
IMO, vacuum advance was originally hooked up to manifold vacuum. Later, the manufacturers hooked it up to ported vacuum for emissions purposes. The big downside of ported vacuum is the engine tends to overheat on hot days in traffic. Ported vacuum will cause the engine to idle with less advance than what it wants. Idle loves advance. It runs cooler and more efficient. From what i've heard, never seen one myself, In the late 60's, in California, they started to install a second vacuum advance that was activated by a temp sensor. I think this was an attempt at fixing the overheating problem. So, when the engine started to overheat it would add additional advance from the second canister and cool the engine. Could be wrong. Just a theory.
Ah, yup. I think you nailed it. That explains the purpose of those (pvc looking coolant switches) perfectly. I do believe, you are spot on. All that foolishness should be bypassed and we should take our vac right from the intake in the first place.
I had a 75 Ford Granada with 302 that had that system smog pump , EGR valve and vacuum hoses everywhere if you took one or two off and did not know where they went your in trouble for sure . It has several water temp sensors with vacuum hoses hooked to it when it got to the set temp it would open and send more vacuum to advance the distributor more timing kinda of a neat idea .
Uncle Tony's Garage: Great video Tony. Retired licence mechanic here. I used two vacuum gauges, one on manifold and other on ported to teach apprentices the difference of the two. Very useful when adjusting the spring pressure and max vacuum advance. Cheers.
Did you go through this issue with your corolla? I'm having issues with my ke55 atm. when advancer plugged into port. the car dies under accelleration. when unplugged completely and port blocked... car runs fine.. lost..
TIMING AND VACUUM ADVANCE 101 by GM Engineer. The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency. The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation. At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph). When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean. The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic. Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it. If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more. What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone. Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam. For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively.
For stock type stuff ported is great, cars form the factory did it that way for a reason.... I had a car with a bigger cam and found it worked best hooked to manifold. The reason why is to get it to idle in gear, I needed the throttle blades open too far causing the idle mixture screws to have no effect. So, hooked to maniflod I got some extra timing that raised the idle allowing me to close the throttle and allowed idle mixture adjustment. This would not have worked if I did not have an adjustable vacuum can the stock cans have too much advance. In full disclosure the stall convertor was too tight for the cam, when I put it into drive the car learched pretty bad. So, yes when modifying engines the combo is very important. This issue is always a debate, IMO the most important thing is to understand timing and the advance mechanisms. Then use a vacuum gage and timing light to actually know how much timing your engine is actually seeing under different conditions. Too many will want to argue about this and they never drove a car around with a vacuum gage or checked their mechanical advance curve. Keep up the good work Tony!! Dont worry about the know it alls, they are just fine. Your are giving a great education to the younger/newer guys!! Its weird to think that there are a lot of 50 year old professional mechanics who never worked with carbs and distributors.
You can also drill a small hole in the front throttle plates, this will allow you to bring the idle screw down to cover the slots in the base plate. If you go any higher on cam profile. Another trick to let a little more air in was to adjust the screw on the secondary shaft to open it letting more air through and accomplishes the same thing. Either will let you drop the Idle screw down to function.
Love it!! First you held class, then when heads started shaking, you took everyone into the lab. "A video is worth a thousand words"...😁 This is basic stuff, dont know how there is debate on it, but you had a great way of clearing the air on the subject Uncle!!👍👍
@@yeboscrebo4451 Hows that??? For people who are unfamiliar with vacuum advance, don't understand it, or might be 'visual leaeners', its totally relevant. How could it not be???
@@wheels-n-tires1846 because the distributor is only part of the symbiosis and doesn’t operate on its own so showing what happens in a disconnected distributor is hardly a comprehensive teaching aid. People think that you can just switch between ported and manifold and “see which one works best”. Wrong. If you switch between one or the other, the initial timing may need resetting, the mechanical timing curve needs resetting, the vacuum advance canister needs to be adjustable and set correctly and finally, even the carburetor may also need adjustment to achieve results. Uncle tony failed to explain WHY time is needed as certain inches of vacuum or certain rpms, he just pointed to a dizzy and said “look, see”. Sorry, even knowledgeable dudes like uncle Tony have crusty ideas they’ve harbored for years that are just wrong.
@@yeboscrebo4451 Lots to unpack there...so first, in other videos hes talked about timing and carb relationships. This vid wasnt about that. It could really be condensed into "see, using this port, good. Using that port, its working backwards, thats bad." Or.... "this shows exactly what happens when you hook it to the wrong hose"... Its meant at a 4th grade level for folks who know little or nothing about distributors, advance systems, carburetors, etc... And Tony certainly wasnt saying you could switch back and forth between ported and unported to run your vacuum advance distributor. Thats idiotic, and nobody that has a clue thinks that. Not sure where you got the idea that anyone thinks that!!! That might be the silliest statement Ive heard on YT in a long time...so its pretty bad!! So anyway, while youre right about the finicky relationships of timing and carburetion, this vid didnt intend to address that. Why does he have to address everything in each video?? Maybe try watching others. Id imagine theres HOURS of Tony on here explaining timing, curves, carburetion, etc. So if you expected it to give a thesis-level dissertation on that relationship and it's details, well guess youll just hafta stay dissappointed, because this vid, and frankly the whole channel seems to be more about basic info and explanations for beginners, or people who only have experience with newer cars and systems. Your conclusion that the old timer is dumping old and incorrect theory on here is whats wrong. I read and used Tonys knowledge for years and years...decades before he ever had a RUclips, and can say that I put together a half dozen street/strip Mopars with that knowledge, and they were better and faster because of it.
@@wheels-n-tires1846 wow that’s a lot of words to not actually refute any part of my comment. Did you ever “unpack” the subject matter of the comment i made? Not sure where I got the idea? Have you read the comment section? Lol. As I already explained, the demonstration was not relevant precisely because it was overly simplistic. To explain the difference between ported and manifold vacuum, it’s not good enough to have a dizzy, removed from the engine, and expect to illustrate the relatively complex interactions between all three forms of advance timing. You can’t just say “look the advance mechanism is moving here on manifold and here on ported” because each case requires changes to the other two forms of timing advance. Just the fact that he did not acknowledge this interaction is indicative of his misunderstanding of the benefits of manifold vacuum advance. It seems like uncle Tony just gotten stuck on the teenage hot rodder “more timing equals faster” approach without every revisiting this idea in his old age. Your better off reading what the actual engineers had to say about it than an old hot rodder stuck in his ways.
My new MSD distributor instruction book said to connect the vacuum advance to the ported vacuum of the carburetor, not manifold vacuum. So, this is what I did, and it works just fine. 😊 Also there are thermal switches that when the coolant temperature reaches 225 deg F the distributor vacuum advance is switched from ported vacuum to manifold vacuum to increase the timing for lower engine temperatures at idle. This was common back before electronic engine controls. These switches can still be found for sale. Or you can do the same thing with a 12 volt three way solenoid valve and a switch. So if you get stuck in traffic in your hot rod you can just flip a switch to help prevent over heating on hot days.
In other words, light load and substantial vacuum implies a less dense charge in the cylinder, and the flame front is moving slower, so the vacuum advance bumps it up so the flame front hits the piston at TDC, which gives more power for that part throttle setting, which in turn enables you to let your foot off the gas even further for better gas mileage.
Hey Tony, I've been dealing with old British cars that not only have vacuum advance but also vacuum retard using a double diaphram distributor. I plug both of them and do what I call a "road tuning". I set it up with the light in the shop and then drive and get the best responsive advance I can on the road, reset idle and call it a day. It's worked for years.
I guess I'm a younger guy, mid 30's. Grew up in the age of distributorless ignition and electronic fuel injection. But the more I watch these videos, the greater respect I have for the engineers of the past for all the clever ways they thought of ways to improve performance, economy, and drivability on an....analog level{?}. The things they did before modern computer power are really quite impressive.
As I recall, vacuum advance is always useful when you have high vacuum because you also have stratified lean conditions. Could be at idle, could be descending a hill, could be light throttle freeway cruise. That vacuum advance is there to help light the very starved almost closed throttle poor mixture, light it early so the weak flame front has time to progress to peak burn. If you watch your own video here as you just presented it, you see that when you accelerated, you were on mechanical advance only, both times. Once because vacuum advance fell back to mechanical only, and once because you ported it. Same result. The vacuum advance can't "remove" mechanical advance. They are separate systems ...
From what I can tell, you are correct. Notice around 4:58 as UT releases pedal, i.e. cruise condition (minimal fuel, somewhat high rpm) the vacuum advance can be seen to go away. But actually, you want mechanical and vacuum all working at that condition as the low cylinder filling and small amount of fuel need max ignition timing. So taking away vacuum advance at the condition, takes away much needed advance. The timing gets taken out during accelaration because cylinder filling increases so a faster ignite happens as a result of the richer mixture. From all the reading plus some testing I've done, I think the issue is that when hooked to manifold going from ported, idle timing goes up too high, so the distributor gets pulled back to end up at the same 12-14° idle timing when it was on ported, but now the vacuum is adding some of that idle timing. But that then limits the higher rpm timing because the mechanical is now down from 12-14, to probably 4 or so (rough numbers for illustration). So when acceleration is applied and vacuum drops, the mechanical is lower than it was when ported as the distributor was pulled back to compensate for the extra that manifold gave it at idle. So if we go back and set timing with vacuum port plugged off, and set say 12° purely mechanical, then plug in manifold vacuum and timing goes up to say 25 (rough number)... Instead of pulling back the distributor, leave it, instead, lean out the idle mixture screws and turn out the idle speed screw. By lowering rpm in this way, it should reduce some of the mechanical advance. Or so goes the theory that David Vizzard puts forth. Effectively, idle timing can be fine on ported but at cruise you want manifold advance to get that high timing number. That's the theory anyway
I think 🤔 the ported was a emissions thing i tried both on my 390 ford and on ported it ran good and the AFR was easy to get 14:1 especially on the Fwy only it woukd get hot 🔥 in stop and go idling traffic in the summer the exaust was 50 percent louder and at startup i would have water vapor coming out of the exaust . On manifold it was alot richer and i would need jet down a size or so alot harder to get perfect AFR usually be around 13:20 ish idling and 13:80 or so on the fwy but if was 50 percent quieter exaust and did not get really hot in traffic . Alot of people say the factory never used full manifold ?. I think before 1975 they did on the valve cover it has a low initial timing like 6-8 degrees if it was ported it would or should say 14-16 degress ...
@@TheThirdWheel618 All of my older vehicles used full manifold vacuum advance except a 1973 Dodge Dart with a slant 6. Once I bypassed the OSAC valve and gave the vacuum advance can full manifold vacuum, the engine ran cooler and more efficient. Better MPG's, better drivability, better cold starts.
@@muziklvr7776 Yeah i think before 75 for sure it was all full manifold Ford had a valve that operated by engine temp you were on ported untill the engine reached a certain temp say 200 then it would shut the valve off and it would go to full manifold to cool the engine down ???? That says it all the factory knows they can reach better AFR with ported at idle but it creates a lean condition so they came up with the valve idea .
Thanks Uncle Tony! There are still a few us gearheads around that remember switching to ported vacuum after "desmogging" a 70s GM product. Power timing with a buddy!
Well, we know the canister works. The distributor has to be curved to work on whichever port you use. If you take a stock distributor that was curved to run on ported and you put it on manifold you will have way too much timing. Likewise, if you plug a distributor into ported that was set up for manifold you won’t have enough. So there is truth in both camps on which is “better”. Best to know what you have for mechanical advance in your distributor and how many degrees at what vacuum your canister delivers to determine what will work for you. Excellent real world practical demonstration from Tony. You won’t get that anywhere else! 👍
I’ve been always using ported vacuum. I’ve had to listen to so many people telling me to run manifold vacuum, but I read something long ago about which port to use, and I’ve stuck with it! The only thing that I’ve done is try to limit the amount of advance, and keep my initial timing up. It’s worked so far, so good! 😉
Great video! I agree, ported, only, ever! I had a great Vocational Auto instructor. We had a Sun distributor machine. He taught me how to use it and to set up and recurve distributors. Must have done 100 over the years. I loved using that and a Sun engine scope, he also trained me on. Fun stuff. A lost art these days.
Tony you are giving me flashbacks, its the mid 1960's auto shop at Martin VanBuren HS Queens. The vacuum gauge was our #1 go to diagnostic tool. Electronic test equipment was years away. I remember buying my first dwell meter and thinking how advanced things had gotten.
1960s car were always ported vacuum to the distributor. Late 70s 80s cars use manifold vacuum with the thermo switch between vacuum port and distributor. I believe some use both to the thermo vacuum tree and delay valves/check valves as this was to delay vacuum advance untell engine was at operating temperature and converter was hot for better emissions.Less timing equals more complete combustion and less oxides of nitrogen. I did state Emissions testing, tuning,rebuilding the computer control carburetors. Adjusing with old Catalytic converters on the vehicle or a cylinder with low compression in one cylinder this was challenging stuff at the time.
The ONLY difference between the two is you don't get vacuum advance at idle with ported vacuum. They both work exactly the same at part throttle and wide-open throttle. Use which ever one makes your engine run best. It will let you know.
Nope. Watch a manifold and ported vacuum gauge side by side and you’ll see that they are not the same at, for example, low load/cruise conditions where the throttle is barely cracked and manifold vacuum is high. When you’re flying down the highway in cruise you need the timing only given to you by manifold vacuum advance. Better mileage and cooler temps.
I think its something that will be debated endlessly. The only way around it is to dyno two cars, one with a factory engine and the other with performance mods. Test both running both ported and manifold and see the power band differences. Love your videos. All the best from Oz
There would be zero difference on a Dyno. You don't leisurely cruise on a Dyno, you crack it wide open under a heavy load--- ported or direct manifold vacuum are BOTH going to give exactly zero added degrees vacuum advance, no partial throttle runs on a Dyno. Glad I drive a truck and don't drive a dyno
@@hiswordheals9710 From what I've read, most modern vacuum advances will give you 12 to 14 advance and mechanical advances will give you 12 to 14. As the vacuum drops, the mechanical advance makes up for it depending on both timing curves. Some mechanical advance only distributors will go as high as 28 to 3,000 rpm or even higher, but mechanical advances are more typical of motors built for heavy load applications such as tall deck 366's or tall deck 427's (extra oil ring in the pistons to handle higher advance/compression/heat at higher RPM's under heavy load). Some vacuum advances are also adjustable so we can play with the timing curve. We know that as RPM's increase, the vacuum increases even as your primary throttle plates open up but as your primary plates open up more than half way, the vacuum begins to drop. I'm spitballing here, but I think the vacuum begins to drop as the primary throttle plates open up past half way but if your engine RPM's are in the high 2000's or higher the vacuum is still mostly maintained so it doesn't drop by much. It's when the secondary 4 barrels (throttle plates) open up that the vacuum tends to crater. Your vacuum advance drops to zero on a SBC with your carb fully open up to around 4500 but then slowly picks up past 4500 advancing minimally by 4 degrees or so around 6500 RPM's. But then, if you are pushing a motor to these RPM's on a dyno, it's built for it. This isn't to say vacuum advances won't be used on the street pushing these revs, but the chances are more likely that a motor on a dyno pushing 6500 or higher is built to race with a lock out distributor with all of it's advance at startup. The type and size of your carb also effects vacuums. A Rochester for example, has much larger secondary venturi and throttle bores than primaries so as your secondaries open up on a Rochester, the ported and manifold vacuums drop lower and more quickly than equal sized throttle bores. Same holds true for larger CFM carbs such as a 750 on a 350 sbc, the vacuum off your port will be lower on a 750 compared to say a 600 CFM carb because your venturi and throttle bores are larger on a 750. Hi performance cams, ported heads and high rise intakes will also drop your vacuum (substantially), but that's for another conversation. 🙂
Uncle Tony, Thanks for tuning me up! It’s been a while since I’ve been in this deep. I’m doing a major rebuild on my ‘79 F100 (bought it new at age 19). Since most emissions parts are obsolete I’ve had to reimagine as best I can. OE vacuum diagrams showed the vacuum advance working off manifold vac, trying to set timing, adjust idle; and it wasn’t making any sense. I think I’ve got it now. I owe you one, or more.
Again, late to this video viewing. Lovin you classroom venue. Was a little worried, bout you being along side the highway with the kind of drivers out there these days. Appreciate the effort, and you managed to show this very “thick headed” guy how this system works. Thank you sir.
My car seems to idle better with the extra timing from manifold advance. It comes off when I hit the gas. So what? It goes back to where I set it in the first place. What am I missing here
Sweet demo rig. I've never thought to try that. Really interesting to see a real world experiment. cheers Unc. My spare sbf points dizzy recently got rigged with a battery, coil and a plug, held to the workbench in the shed by a chunk of railroad track and spun up with a skateboard wheel with a silicone hose tyre mounted in the drill. Mission was to calibrate the new old been in bits custom tach. Works a treat. Dead nuts on to the digi timing light tach after tweaking it. Some people would have rigged up a signal generator circuit but analogue with dangerous fizzing taser sparks way more fun. Even the wife was impressed.
I changed the cam on my 350sbc and had left the vacuum at ported. It ran good set at timing and everything. I read up about how ported was made for pollution control and hindered car performance at idle. I changed it to manifold vacuum the other day and holy shi*!!! The car ran better, idled better, and drove well overall. I decided to play around with the timing a little and move my distributor a tad bit more with manifold vacuum and damn I got even more kick out of the mouse. Didn’t know how much performance I was leaving at the table with just one darn vacuum line.
This channel is a gold mine. I learn something every video. I always thought vacuum advance's were always connected to manifold until the early 70's when they switched it to ported because it allowed for better emissions. My understanding was that if I want better emissions I should do ported, but if I want better drive-ability I should do manifold.
Yes ported it runs hotter so it will burn off the fuel more although in stop and go traffic in the summer you can get into trouble running ported . I ran ported and I could get 14.7 or more on the AFR gauge idling on manifold I would stumble out past 12.9 or so less timing the leaner it is more timing the richer it is problem is the distributor is not tuned for manifold vacuum a adjustable pod is a must .
The difference is absolutely not opposite. The only difference is you have no vac advance at idle. Off of idle it is the same. The question is what do you want at idle. And the answer is not the same and every condition.
I always learn something when I watch Uncle Tony. Hard learned knowledge that he's willing to share. Thank you for taking the time to teach and entertain.
Good simple explanation. Using manifold vacuum you are defeating the whole purpose. I could do a whole video on this myself. I've read many of the comments here and many have no clue. Back in the day (maybe they still do) they had those Sun machines that you could fine tune a distributor. Change centrifigal springs if need be for certain RPM advance so no vacuum needed. A lot of people don't know that some vacuum advance cannisters are adjustable through the vacuum port with an allen wrench.
Excellent explanation. Most people overcomplicate these things because they don't understand fully what they are talking about. The simplicity of this demo speaks for itself
The demo is TOO simple. He showed what happens to the dizzy when the advance canister is hooked up to ported or manifold. He didn’t adequately explain why you need different timing at different levels of load or rpm. For a more comprehensive demonstration, the dizzy needs to not be removed from its symbiosis with the other parts of the engine. A better approach would be to show two different vacuum gauges one from ported and one from manifold at the same time. Then, take the engine through different circumstances in load and rpm to show what is happening with the timing. Uncle tony was able to explain the opposite of the truth because his demo was overly simplistic.
You explain everything so well but there's always someone who wants to disagree with what you have to say, which is from many years of experience. Most of them probably never even turned a wrench! Thank you Professor Tony! 😎
Is this backward for just me or a bunch of people? I thought manifold vac was better for big cam engines to help smooth out idle. To date everything I have read has always said manifold vac advance is the way and that ported was only good for some mopars and later used as a crutch for the gas crunch smog era emissions. Great video as always demo is excellent. Maybe I need to go flip some hoses around and save some at the pump due to more mpg. Thanks for the knowledge!!
There will be spring or weight differences on a stock distributor, depending on whether they want to emphasize street performance, track performance, economy, or emissions. You can alter those goals by changing total vacuum (different can or link), and/or by changing the centrifugal springs or limiting the travel of the weights (more difficult). Just remember if you limit vacuum advance or weight travel, you may need to alter idle timing to ensure higher rpm advance while cruising is not way off. You might also find a deceleration solenoid (or vacuum device) that prevents the throttle from slamming shut and sending manifold vac to over 25, causing timing to advance when it would drive emissions highest (you're not interested in performance when decelerating anyway but Uncle Sam is particularly interested in emissions at that moment). Salute that solenoid, it's a good soldier. But when you are part-throttle accelerating your 70's Dodge and interested in performance for a few seconds, there's a traitor called the OSAC Valve (usually hanging off the air cleaner body) interrupting the vacuum hose from the carb to the distributor. That thing prevents vacuum advance for several seconds while accelerating, and since you just left the stop sign, your revs are not high enough to give centrifugal advance, so with timing delayed you end up pushing the pedal way down to keep up with the 60's car beside you (no OSAC delay). Sound familiar? Bypass that OSAC, plumb the vacuum direct to the distributor.
Off idle response and cooler running engine have nothing to do with performance? Don’t think so. There is a lot going on with a mechanical distributor, springs and weights, mechanical advance degrees, vacuum advance degrees, response adjustable and non adjustable vacuum cans. Most people don’t have the time or energy to dial in and tune a mechanical distributor let another understand how it all works together. It’s hard to explain, I have tried every which way with my olds 350 and 350 sbc, hands down manifold for me.
I'm a huge fan of manifold vacuum and I can see many benefits on my 41 Chevy inline 6, since I swapped it over to manifold. Especially mileage and temperature. What a lot of folks saying : ported came with emission in the 60s is a myth though - my 41 had ported from the factory, some cars even earlier - why? I don't know, since the engineers back than must had have something in mind - but that would be an other interesting discussion.
Sorry. Ported vacuum is for smoggers. At idle and low throttle the mixture is lean and needs advance. Smog distributer curves had tons of advance, like 12*, at idle to compensate somewhat for the ported vacuum advance. They did this to make the car run hotter. My 68 L36 Corvette used 4* initial and full manifold vacuum to the cannister.
Correct. The ported vac would be exactly the same as manifold vac anytime off idle. So manifold vac would allow more advance at idle and for longer burn times needed at idle. Plus low base timing for ease of start before building vac
This confuses me. Wouldn’t you want timing advance at high vacuum/low throttle situations? There is almost no port vacuum when the throttle is at or near idle.
Basic. Ported. Manifold give an unstable. Step on the gas and timing drops out. Big cam, put it in gear, vac drops out. Idle.surge.on cam at idle, timing drops out, wants to stall. Manifold is not what you want.
Yep, mostly mechanical can be good too, especially if it's a race car or constant heavy load too, where there's not much vacuum signal. A vacuum can that comes in fast with not much vacuum doesn't drop out as quick, or only drops out just a small amount (mechanically limited) might be fine running on manifold vacuum. GM for instance probably used near 30 different vacuum canisters on the many applications, both manifold and ported were used. Later vehicles with emissions were mostly ported and earlier, especially performance, were manifold. General vanilla in 70's ported was quite common.
Dont you guys realize its the same thing as soon as you step on the gas there is zero difference between port and manifold, port vs manifold affects idle only
@@researchandbuild1751 If your can never moves, or moves full advance, there's a difference. For instance, a can that's calbrated for all-in @ 18" will likely produce a different result than a can that's all-in @ 8" vacuum, right?
sometimes i like to use manifold vaccum with a cammed engine. it tends to keep the fenders from shaking off it but usually i just end up not useing the vac advance.
@@boss351gt6 well running it on manifold vac just makes it run smoother the when you stab it. vac drops n you revert to mechainical advance. only really food for cruising n idle
I've played the ported / manifold vac game before. In the end both of my cars are still on ported. With a properly set up dist., initial and total dialed in, ported is where it's at. Much smoother part throttle acceleration.
Part throttle acceleration is the domain of initial/mechanical but mostly mechanical advance. Ported timing is redundant in this regard - it’s doing the same job as mechanical timing just a more limited range. Use manifold advance and you free up the vacuum canister to do a different job that ported is unable to do - advance timing at high vacuum/low load situations.
Sorry Tom, I couldn't see ANYTHING moving in the distributor at all. As a side note, I love your channel & your old school style & have learned a great many things from you in the past. Thank you Tom. Len from Canada.
Great work as always Tony, clear and concise answers and demonstrations that clear the air and give actual information that is physical and tangible for everyone to see and more easily understand the concept. Nicely done sir
Not totally correct there sir. When base timing is set properly, you need to have the vacuum line disconnected and plugged. Then once it's set, you can plug back in the vacuum line to your distributor. With it connected to full manifold vacuum, You will have a lot more advance at idle. Some motors like this setup. The motor will run cooler and not as lean. You will have to adjust your idle screws down which is a benifit in some cases as now your motor is less likely to diesel when shut off. Also your idle mixture screws will be more functional if they weren't before. Once you began accelerating the amount vaccum advance will drop some as in your video due to less vaccum in the intake manifold from throttle plates opening. Except it will still be the same actual amount of advance as if you had it connected to ported vacuum. The ported provides no advance at idle so the motor runs hot, and lean. It will make cleaner emissions this way. When you accelerate the ported timing port then applies vacuum to the distributor and advances the timing at that time, but it's to the same amount it would be if it was connected to straight manifold vacuum. The amount of vacuum advance does not change depending on rather it's hooked up to full manifold vacuum, or ported. The only difference is full manifold vaccum will give you more of that advance while at idle, where ported waits until part throttle. Both will have the same timing at part throttle cruising and WOT.
Thanks Tony Best explanation. I am a visual type of leaner not reading a book or explaining the function and not showing how this function actually works while in use.
76 vette came with 6 BTDC, Vac Adv to Manifold. If sVac. Adv. is switched to ported, vehicle will overheat at idle, running soley on initial 6 BTDC. Vac Adv. dies off at throttle but timing springs/weights compensate for the draw down. This cannot be seen in your example as the distributor is not rotating. When throttle is close to a cruise, initial timing,vac adv. timing, and spring timing are all incorporated for better fuel economy.
One advantage to using timed vacuum advance is that an engine with conservative ignition timing, has better engine braking than one with generous ignition timing. Nice thing to have in hilly areas!
It really takes a really knowledgeable and has some common sense mechanic to dumb this stuff down to this level. I admire your patience with the keyboard warriors.
Uncle tony I love your videos. Hi from Australia. I feel if people are not up to speed with basic things like vacuum advance, Mabey they should choose a new hobby. But then I remembered we all have to start somewhere. So. For the young blokes who watched this I thank you. You will teach them
Thank you for all the great info and breaking everything down step by step, and for free to everyone who wants to learn the right way and understand how and why for every video you make. Thank you
So doing a lot of reading on this subject. With leaner mixtures you want more advance for a full burn. And as the mixture richness increases you want the timing retarded since the higher cylinder pressure doesn't require as much time to burn as a lean mixture. So wouldn't that mean the most efficient burn is happening with manifold as ported is making for a less efficient burn and higher exhaust temps? Which is putting more stress on the motor with more heat?
I have certainly seen both sides pointed out. However doesn't this demonstration just show Vacuum Advance going away as the vehicle is accelerated. You would still be left with the same amount of Initial+Mechanical. Does that extra advance dropping out quickly cause a negative performance issue and is there MPG benefit to having that extra timing during idle?
Man wish I had know this some 30 years ago. Completely understand the difference between ported and manifold vacuum. Now that explains why it never ran as good as it should have.
This is very good. The vacuum system is overlooked by many and understand by a few people. Remember, your knowledge is not the same that other people have or think they know.. People start off wrong and the stay wrong. It takes some person like you ( Has credibility) to head people in the right direction. Thanks again
So at light cruise in hunts for the highest manifold vacuum and allows for the best fuel economy. At high-altitude we add a few degrees of base timing and move the vacuum advance to ported. This allows for a smoother idle and leams the carburetor out by raising manifold vacuum and allowing the power valve to pull slower. There is also a third vacuum source called the venatori vacuum. This vacuum source is used only to control EGR through Chrysler's famous EGR amplifier mounted on the firewall.
I've was taught to do my timing with the vacuum advanced off and then attach the line to the port on the base of the carburetor, never thought that much of which side to have the distributor to get its vacuum from, I've always put the line to the carburetor ports, if on the manifold vacuum tree then cap it and place it to the carburetor.
Hello Uncle Tony, Thank you very much for all the information you have given us. 1st Oct, 2019 I bought a 65 Mustang that needed everything so I could learn about these things we drive every day. RUclips and manuals have taught me much but there are things that slip through the cracks here and there that I have to catch as aside note in some video about something completely unrelated. Then I found your channel. Your so direct and actually bother to put into video format your advice and knowledge. I understand how actually bothering to set up, film, edit, and post is a time-consuming process. So again, I thank you for taking the time to put your experience into RUclips so green mechanics like myself can learn. I have a small request and if a video has already been made then please if anyone could point me in the right direction I would be most gracious. You had spoken briefly about how your lifestyle is in your cars. Specifically, you don't keep cars with really high-end paint jobs because of the upkeep a super high close finish requires. I have been trying to discern what you do to paint your cars by looking at your cars in your videos. What do you recommend as a paint job for a daily driver classic? So far I have done all the prep work, then primer, blocked it, then base coat, and blocked, then matte clear with hardener. What would be the simpler way for daily driver upkeep? Thank you again for everything.
Friends 350 Nova, when he changed manifold and carb ran tired. After talking he showed me how the install info said to use manifold. I switched it to Venturi and after having to replace the vacuum advance unit car ran great. Manifold vacuum had separated the diaphragm. Never did use manifold on anything but the wipers and heater switch
I'm confused. You demonstrated what happens when you get ON the throttle on manifold, but then demonstrated when you get OFF the throttle on ported. what does ported do when you get ON the throttle that makes it better?
The one area I still struggle with is why to use port vacuum, like Tony suggests, when the distributor weights and springs were designed to advance the timing mechanically under throttle? Why would the car manufactures design both types (mechanical and port) to advance the timing when one can do it by itself. The explanation on using manifold vacuum makes more sense to me because under cruising (part throttle), the air fuel mixture, which is less dense, needs more advance timing to allow the mix to burn efficiently, making the car run cooler and smoother. Advancing the timing under this driving condition can only be achieved through manifold vacuum. So, the system uses manifold vacuum at idle to low speeds then switches to mechanical advance when under acceleration, keeping correct timing under all driving conditions, thereby negating the need for port vacuum all together.
Exactly. Ported timing is redundant. Its performing the same function as mechanical just laid over the top of it. Manifold advance gives you what ported can’t - timing in conditions of high vacuum/low load when your engine needs it. Uncle Tony has this crusty old idea lodged in his brain and doesn’t revisit or question the old beliefs he’s been harboring for decades. Classic old person.
Of course now I'm contemplating hooking up some kind of valve to both ported and manifold vacuum with some sort of cable or solenoid to switch between the two. :)
Should be added that some advance canisters can be adjusted with a tiny hex wrench up the vac tube to adjust how much timing the canister gives. Aftermarket "performance" canisters typically have this feature.
Yes , I bought an adjustable vacuum advance for my 75 Caddy and kept a little allen wrench available so I could adjust my vacuum advance at Cruise or if I was Towing a very heavy load with 87 octane . I recurved the distributor timing with different springs and different factory GM weights in addition to the adjustable vacuum advance. I think the vacuum canisters that have the hexagonal instead of the round bodies have a plate in there that the adjustment screw goes through and that screw can give more or less pressure on the spring that the vacuum diaphragm pulls against- I'm not sure if the round ones are adjustable or not. My buddy bought a Mopar electronic ignition conversion kit for his 69 roadrunner and I remember the instructions were pretty cool and thorough and how to setup the vacuum and mechanical advance for performance and mileage. I think going back twenty years ago it said to set up the mechanical advance first (with the vacuum advance disconnected) by doing I think it was second gear acceleration runs to optimize performance without pinging or detonation . And then after you had the mechanical advance optimized you would hook up the vacuum advance and adjust that for driveability and mileage.
I disagree. You want the vacuum advance at idle and part throttle cruising; however, you want it to drop off under full throttle acceleration to prevent detonation. One reason why you want it at idle is so you don't need as much base timing (around 10° or so) for easier starts, but still hit around 26° or so at idle after it starts, allowing it to idle much better. The vacuum advance is for fuel economy at idle and crusing, as well as for easier starts by allowing the base timing to be set lower. The vacuum advance should have no bearing on total timing at full throttle, high load, low vacuum conditions. With base timing + mechanical advance, you should have enough timing for full throttle acceleration just before pre-ignition, independent of vacuum advance. At cruising, you want much more timing when the load on the engine is low and the risk of pre-ignition is pretty much non-existant; hence, base+mechanical+vacuum cruising you should see about 54° or so, but only about 36° give or take at full throttle, high load conditions, where the risk of pre-ignition is high (which is why you want it to drop off, not come in). When using the timed port, you're not seeing any of the idle benefits you could be, and your base timing has to be set higher to get a good idle, making it harder to start. Original vacuum advance setups were on full manifold vacuum from the factory up until sometime in the early 70s I believe, when emissions regulations began to have much more bearing. I'm not sure what the thinking was behind the change, I just know there was a change. But just running on base timing doesn't give the engine the amount it wants at idle; where again, the risk of pre-ignition is pretty much non-existant provided the carb is tuned correctly for the right amount of advance at idle. You can see numbers and management philosophies like these when looking at ignition tables for fuel injected engines; even on my '98 vortec 350 (just a gen1 small block,) the stock ignition mapping is like this.
Hi uncle tony, very good video I’am learning how to set up a engine your way . I’m self taught working on cars for along time I don’t know everything I wish I did at 71 years old just keeping at it I like working on cars thank you for all your help 👍🚘🔧
Tony, love your channel. I’ve got a 70 GTX with a 440. The bottom end is stock, the top end, I added trick flow power port 240 heads, and Edelbrock performer RPM intake, an Edelbrock performer 800 CFM carb, a Comp cams 491 lift hydrologic flat tappet cam, 236 duration @50, Howard’s lifters, TTI 1 7/8 headers and 3 inch exhaust. I built it to be a fun dependable cruiser. The car had points ignition before I pulled the top end apart. The engine was completely rebuilt 2,000 miles ago btw.... I bought a summit electronic conversion ignition kit. I started the car and I couldn’t get it to idle, it’s an automatic and when I put it in gear, it died, or was terrible. I bought a JEGS distributor and their ignition box, better but not good. I sent in the summit distributor to have it put on a sub machine by a guy in Ohio. He asked for my cam and gears and compression (10.5:1) ratio. He promised the world, well, it made it worse. Wouldn’t rev over 3,000 rpm. Oh, on the manifold side, it’s pulling 13 inches of vacuum at idle but on the port side, it’s pulling 5 inches. That doesn’t seem right. I heard about FBO ignition. Don said his system runs off the manifold side. I installed his system, it’s much better but but when I connect the vacuum to the carb, it starts popping through the exhaust like crazy. When I run it without the advance hooked up, it’s pretty good but still not perfect. I’ve been watching your channel for awhile now. You’ve forgotten more than I know and I’m pretty good with mopars. I would really love your take on this. Thanks Uncle Tony!!!!!
It’s your carb. Or something with your idle speed screw. You should not get ANY vacuum of your ported side of your carb. It should be at 0. If you can’t get it to idle it sounds like your initial timing is off. Quick way to find out if it’s off is to plug your distributor to manifold. If it idles better then yes your initial is off. Manifold adds timing at idle so that’s one way to see if that’s your problem.
Its more complicated. It really depends on how it was setup from factory. For example. if distributor does not have mechanical advance, than using ported vacuum advance is how its done. Also how it vacuum advances different on different era distributors.
What I found with my car is that it required less throttle opening to maintain a good idle with manifold vacuum. With ported, I had to have the throttle open more, no big deal, except that the car tended to run on and diesel when I shut it off. Your results may vary.
Sounds like you are not tuning your carburetor correct. To lower your idle speed, you need more air to bypass the throttle blades. Opening the secondary blades a slight amount, or drilling the primary blades. The idle circuit alone, may not supply enough air for a good running idle. The added air will allow you to close the primary blades and the idle circuit will function properly. Please read HP books Holley carburetor manual. Your welcome..... .
Well on my 70 Buick Lesabre with 350, I swapped the vac hoses around on my thermal vacuum switch. I saw I was running full manifold vac on the dist. The bottom port on the drivers side on my quadrajet had no vac unless I worked the throttle. So I mistakenly criss crossed them. When I made the switch, it was a much smoother ride and swifter kick in the pants when accelerating. When the car is idling hot during heavy traffic, the tvs plunger is supposed to shoot up and block off the ported and allow manifold to help cool off the engine with higher rpm... I realized something was wrong when my engine really bogged down when it got over 190 deg. But now, my engine runs much cooler.
This is the first time I’ve ever seen this explained well
with out taking an hour, straight to the point...Thanks
I read an article by one of the engineers involved with designing these systems, he knows what he is talking about and says you always want to use full manifold vacuum. It keeps your engine cooler at idle due to the added advance, and has other benefits as well. Ported was something that was used later on to attempt to help emissions.
No. Lots of timing at idle creates heat.
correct. At idle, It will run smoother, cooler, create higher vacuum and run leaner increasing mileage.
Tony couldnt you find a busier😅 street to film on?
You, sir....... are correct.
I have not run across an engine yet that performs better with ported vacuum than manifold vacuum. Ported was an emissions era crutch from the early 70s. All the 60s engines used manifold vacuum.
my 1987 Honda CRX came from the factory as manifold vacuum. Had many people tell me to change it to ported instead of manifold. Pretty much ran the same at cruise, but at idle it was terrible, and would start overheating because of how hot the headers were getting on ported vacuum (about 5 or so degrees of timing (no vac, no mech) ), manifold vac would put it at around 20 degrees of timing (vac timing, no mech) and idles incredibly smooth
@@cmdr_scotty yep. My engine cooled down and ran super quiet when i switched to manifold.
Ford used ported in the 60's so......
@@yeboscrebo4451 same with my 350!
Exactly.
Love the sounds of an old Dodge...the door latching, the hood groaning...I can almost smell the OEM musty smell..👍😂
Maybe that wasn't the car? Need to consult with Al's wife Peggy on this one. ;)
@@thisisyourcaptainspeaking2259 savage...😂
Not my old Mopar's..Mopars were always tighter and rattle free than GM/Ford..unless you only owned 400,000 beaters that were slapped with new paint!
@@wheels-n-tires1846
An old timer once told me:
If it smells like fish make it a dish.
If it smells like cologne leave it alone.
@@MrTheHillfolk haha. Love it. Always avoided the gals with too much cologne.. What they trying to hide...
Switching to manifold vacuum cured almost all my problems. New rebuilt 350 stock except for an RV cam. New holley 600. new MSD distributor the list goes on and on.. Never could get it to idle correctly no matter what I did. 14 degrees btdc. Finally read that article, switched to manifold vacuum and its like a new car. It runs and drives so much better its unbelievable.
Yeah, uncle tony is wrong on this one. Listen to the actual automotive engineers describe the purpose of manifold vacuum advance. Tony has it backwards
@@yeboscrebo4451 link?
@@theungoliant9410 I’m sorry I don’t have one. You’ll have to run a search on the subject. I’m sure it won’t take long to find - it didn’t for me when I dug into the subject. There were two engineers in particular who have written extensively on the subject. If I remember correctly, one of them was a former GM engineer. Very interesting information
Same thing ... I switched to manifold and it's suddenly running so much better, it's unbelievable. Idles perfect, and you you tap the throttle, it just wants to go. For 40 years I've always done manifold from American Chevy 350s, Ford 289s, most European cars. Today many advice ported so I've been having a go at that. Nope. just doesn't work for a normal daily driver car with traffic choked roads in my hot tropical country.
@@theungoliant9410 ruclips.net/video/Y69OGBb0GGw/видео.html
Vacuum Advance plays a huge part in Fuel mileage... I have found on my tunnel ram setup I get better driveability from Manifold vacuum.. you can use adjustable vacuum pots so you can dial in your vacuum advance and have your cake and eat it too....
2-3 MPG and a Fan Clutch on the street almost the same. Big difference on MPG added up.
I just made the switch to manifold on my 72 f350. Of course I had to make plenty of adjustments with timing but it was far superior to ported. The first thing I noticed was how quiet it was on a cold start. The engine ran much better and my mpgs went up by 3. I just don’t get why you’d want to run ported
One thing Tony doesn’t mention is, retarding timing under throttle can prevent detonation which can be a good thing in a performance engine. I run manifold vacuum and got a smoother idle and it stopped pinging at WOT.
I get that too, far superior performance and driveability on manifold vacuum. This debate will continue on, at the end to each his own. I'm happy always with manifold vacuum.
Absolutely correct. The biggest problem is that the off-the-shelf distributors have too much mechanical advance for ported vacuum. I had DUI build me a distributor with 12 degrees mechanical advance and a 14 degree vacuum canister. I start with 24 degrees initial timing which using ported vacuum is your idle timing. But I vary that from about 22-26 degrees as needed. So this gives me 24 degrees at idle, 36 degrees total timing and 50 degrees light load cruise which is exactly what a first generation SBC wants. My engines all run perfect.
For Ported Vacuum
Idle 24
> 12 mechanical advance
Total 36
> 14 vacuum advance
Cruise 50
DUI recommends manifold in their literature. How many of those 14 degrees ported vacuum advance are you getting at high speed/low load cruise? At low load, manifold vacuum is high and ported is quite low obviously. Run two gauges at once to validate. Seems like you could be getting more mpgs out of your cruise with more timing, manifold timing.
it’s all the same except at idle and WOT (wot has no vacuum anyways so it’s a moot point). Manifold has higher timing advance at idle, lower EGT’s and not as good emissions, then pulls timing as the throttle blades are opened. Ported vacuum has no advance at idle, because it sees no vacuum at idle. As the throttle blades are opened, the vacuum rises and it adds timing advance. The way that you determine which is best is the way your distributor curve is set up, and your application. Some guys will swear by ported only, others by manifold only. If you have the ability to use a dyno I’m sure there’s a negligible difference in part throttle power, because in the middle of the part throttle operation, with the manifold vacuum advance dropping and the ported rising, they intersect at the same amount of advance. So, to sum it up, they achieve the same effect, just one adding timing and one taking timing out. The engine will run differently on each due to the way they add or remove timing. Remember, this is only idle and vacuum cruising, wide open throttle doesn’t matter for vacuum advance.
6 of one half a dozen of the other.Your description is pretty spot on i think.
I remember having a '71 ford fe that had a coolant temp vacuum switch that when coolant temp got to a determined level it would route manifold vacuum to the dist. in order to increase timing and raise idle speed.That car detonated like mad on any kind of a part throttle load and started my education of vacuum advance. I remember trying so hard to keep the vacuum advance and tune out the detonation cause why I don't know.... because i was giving up maybe a mpg in fuel economy i guess LoL
I thought the only difference between full vac and ported was having extra advance at idle. Ported timing waits until throttle is just off idle to work. So it makes no difference either way. The power and fuel economy is the same. The only change from the exta timing at idle is smoother idle, cooler temp, better vacuum assist to power brakes, ect. depending on your engine combo, it may run better at idle. The higher vacuum signal lets you lower the throttle plates even more to gain better results from your idle mixture screws. Remember, we always set our base timing and and check max timing with the vacuum advance disconnected anyway. WOT doesn't use vacuum advance, so there should never be a change in performance. Anyone who disagrees must be setting their base timing with vacuum advance connected. This is wrong and will affect many things negatively. Love your videos, Tony!
Well said Ed. Full manifold vacuum is the best way. I think ported started with the Clean Air Act in 68.
Ported vacuum is pretty low just off idle and manifold vacuum is pretty high just off idle. You’re getting much more advance with manifold in that situation. It’s not just idle where the difference is. In fact, most vacuum canisters I’ve come across don’t start advancing timing until about 5 hg. So if your canister is connected to ported and you’re in light cruise with those throttle blades barely cracked, you’d be getting zero advance. If you were connected to manifold you’d be getting all of it - like you should.
IMO, vacuum advance was originally hooked up to manifold vacuum. Later, the manufacturers hooked it up to ported vacuum for emissions purposes. The big downside of ported vacuum is the engine tends to overheat on hot days in traffic. Ported vacuum will cause the engine to idle with less advance than what it wants. Idle loves advance. It runs cooler and more efficient.
From what i've heard, never seen one myself, In the late 60's, in California, they started to install a second vacuum advance that was activated by a temp sensor. I think this was an attempt at fixing the overheating problem. So, when the engine started to overheat it would add additional advance from the second canister and cool the engine. Could be wrong. Just a theory.
Ah, yup. I think you nailed it. That explains the purpose of those (pvc looking coolant switches) perfectly. I do believe, you are spot on. All that foolishness should be bypassed and we should take our vac right from the intake in the first place.
It’ll only overheat if the manufacturer didn’t design enough static advance in, or the idle jets pushing the whole lean burn thing way too far.
I had a 75 Ford Granada with 302 that had that system smog pump , EGR valve and vacuum hoses everywhere if you took one or two off and did not know where they went your in trouble for sure . It has several water temp sensors with vacuum hoses hooked to it when it got to the set temp it would open and send more vacuum to advance the distributor more timing kinda of a neat idea .
Uncle Tony's Garage: Great video Tony. Retired licence mechanic here. I used two vacuum gauges, one on manifold and other on ported to teach apprentices the difference of the two. Very useful when adjusting the spring pressure and max vacuum advance. Cheers.
this guy is the best classic engine teacher on the internet. I've learned so much here
Did you go through this issue with your corolla? I'm having issues with my ke55 atm. when advancer plugged into port. the car dies under accelleration. when unplugged completely and port blocked... car runs fine.. lost..
When I was a kid, my mother was being shown a vacuum gauge. She then sucked on it and seemed very proud. I had no idea why....
WTF? LOL
Baaark
@@AustinRBa could be they ignited an advancement
Tell your mom i want my gauge back dammit...........
I may know your mom
I wish there were some sort of marks to be able to see it move. Maybe it’s by old eyes not being able to see anything move
Me either.
Definitely not just you! I had to zoom and stare and rewind a little.... finally saw it. Phew!
We are not alone
TIMING AND VACUUM ADVANCE 101 by GM Engineer.
The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.
The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.
At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).
When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.
The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.
Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.
If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.
What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.
Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.
For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively.
I love how you make the explanations so very simple by just physically showing it actually doing what it does.
For stock type stuff ported is great, cars form the factory did it that way for a reason.... I had a car with a bigger cam and found it worked best hooked to manifold. The reason why is to get it to idle in gear, I needed the throttle blades open too far causing the idle mixture screws to have no effect. So, hooked to maniflod I got some extra timing that raised the idle allowing me to close the throttle and allowed idle mixture adjustment. This would not have worked if I did not have an adjustable vacuum can the stock cans have too much advance. In full disclosure the stall convertor was too tight for the cam, when I put it into drive the car learched pretty bad. So, yes when modifying engines the combo is very important.
This issue is always a debate, IMO the most important thing is to understand timing and the advance mechanisms. Then use a vacuum gage and timing light to actually know how much timing your engine is actually seeing under different conditions. Too many will want to argue about this and they never drove a car around with a vacuum gage or checked their mechanical advance curve.
Keep up the good work Tony!! Dont worry about the know it alls, they are just fine. Your are giving a great education to the younger/newer guys!! Its weird to think that there are a lot of 50 year old professional mechanics who never worked with carbs and distributors.
You can also drill a small hole in the front throttle plates, this will allow you to bring the idle screw down to cover the slots in the base plate. If you go any higher on cam profile. Another trick to let a little more air in was to adjust the screw on the secondary shaft to open it letting more air through and accomplishes the same thing. Either will let you drop the Idle screw down to function.
Love it!! First you held class, then when heads started shaking, you took everyone into the lab. "A video is worth a thousand words"...😁
This is basic stuff, dont know how there is debate on it, but you had a great way of clearing the air on the subject Uncle!!👍👍
The demonstration was hardly relevant
@@yeboscrebo4451 Hows that??? For people who are unfamiliar with vacuum advance, don't understand it, or might be 'visual leaeners', its totally relevant. How could it not be???
@@wheels-n-tires1846 because the distributor is only part of the symbiosis and doesn’t operate on its own so showing what happens in a disconnected distributor is hardly a comprehensive teaching aid. People think that you can just switch between ported and manifold and “see which one works best”. Wrong. If you switch between one or the other, the initial timing may need resetting, the mechanical timing curve needs resetting, the vacuum advance canister needs to be adjustable and set correctly and finally, even the carburetor may also need adjustment to achieve results. Uncle tony failed to explain WHY time is needed as certain inches of vacuum or certain rpms, he just pointed to a dizzy and said “look, see”. Sorry, even knowledgeable dudes like uncle Tony have crusty ideas they’ve harbored for years that are just wrong.
@@yeboscrebo4451 Lots to unpack there...so first, in other videos hes talked about timing and carb relationships. This vid wasnt about that. It could really be condensed into "see, using this port, good. Using that port, its working backwards, thats bad." Or.... "this shows exactly what happens when you hook it to the wrong hose"...
Its meant at a 4th grade level for folks who know little or nothing about distributors, advance systems, carburetors, etc... And Tony certainly wasnt saying you could switch back and forth between ported and unported to run your vacuum advance distributor. Thats idiotic, and nobody that has a clue thinks that. Not sure where you got the idea that anyone thinks that!!! That might be the silliest statement Ive heard on YT in a long time...so its pretty bad!!
So anyway, while youre right about the finicky relationships of timing and carburetion, this vid didnt intend to address that. Why does he have to address everything in each video?? Maybe try watching others. Id imagine theres HOURS of Tony on here explaining timing, curves, carburetion, etc. So if you expected it to give a thesis-level dissertation on that relationship and it's details, well guess youll just hafta stay dissappointed, because this vid, and frankly the whole channel seems to be more about basic info and explanations for beginners, or people who only have experience with newer cars and systems. Your conclusion that the old timer is dumping old and incorrect theory on here is whats wrong. I read and used Tonys knowledge for years and years...decades before he ever had a RUclips, and can say that I put together a half dozen street/strip Mopars with that knowledge, and they were better and faster because of it.
@@wheels-n-tires1846 wow that’s a lot of words to not actually refute any part of my comment. Did you ever “unpack” the subject matter of the comment i made? Not sure where I got the idea? Have you read the comment section? Lol. As I already explained, the demonstration was not relevant precisely because it was overly simplistic. To explain the difference between ported and manifold vacuum, it’s not good enough to have a dizzy, removed from the engine, and expect to illustrate the relatively complex interactions between all three forms of advance timing. You can’t just say “look the advance mechanism is moving here on manifold and here on ported” because each case requires changes to the other two forms of timing advance. Just the fact that he did not acknowledge this interaction is indicative of his misunderstanding of the benefits of manifold vacuum advance. It seems like uncle Tony just gotten stuck on the teenage hot rodder “more timing equals faster” approach without every revisiting this idea in his old age. Your better off reading what the actual engineers had to say about it than an old hot rodder stuck in his ways.
My new MSD distributor instruction book said to connect the vacuum advance to the ported vacuum of the carburetor, not manifold vacuum. So, this is what I did, and it works just fine. 😊
Also there are thermal switches that when the coolant temperature reaches 225 deg F the distributor vacuum advance is switched from ported vacuum to manifold vacuum to increase the timing for lower engine temperatures at idle. This was common back before electronic engine controls. These switches can still be found for sale.
Or you can do the same thing with a 12 volt three way solenoid valve and a switch. So if you get stuck in traffic in your hot rod you can just flip a switch to help prevent over heating on hot days.
Class is in session, pay attention.Thanks UTG. Stay safe, God Bless
In other words, light load and substantial vacuum implies a less dense charge in the cylinder, and the flame front is moving slower, so the vacuum advance bumps it up so the flame front hits the piston at TDC, which gives more power for that part throttle setting, which in turn enables you to let your foot off the gas even further for better gas mileage.
Yes, that’s what manifold vacuum advance gives you, not ported
Hey Tony, I've been dealing with old British cars that not only have vacuum advance but also vacuum retard using a double diaphram distributor. I plug both of them and do what I call a "road tuning". I set it up with the light in the shop and then drive and get the best responsive advance I can on the road, reset idle and call it a day. It's worked for years.
I guess I'm a younger guy, mid 30's. Grew up in the age of distributorless ignition and electronic fuel injection. But the more I watch these videos, the greater respect I have for the engineers of the past for all the clever ways they thought of ways to improve performance, economy, and drivability on an....analog level{?}. The things they did before modern computer power are really quite impressive.
As I recall, vacuum advance is always useful when you have high vacuum because you also have stratified lean conditions. Could be at idle, could be descending a hill, could be light throttle freeway cruise. That vacuum advance is there to help light the very starved almost closed throttle poor mixture, light it early so the weak flame front has time to progress to peak burn.
If you watch your own video here as you just presented it, you see that when you accelerated, you were on mechanical advance only, both times. Once because vacuum advance fell back to mechanical only, and once because you ported it. Same result.
The vacuum advance can't "remove" mechanical advance. They are separate systems ...
Exactly. "When you need it most-" it was *never there* in the ported scenario- how can it be "taken away?!"
From what I can tell, you are correct. Notice around 4:58 as UT releases pedal, i.e. cruise condition (minimal fuel, somewhat high rpm) the vacuum advance can be seen to go away. But actually, you want mechanical and vacuum all working at that condition as the low cylinder filling and small amount of fuel need max ignition timing. So taking away vacuum advance at the condition, takes away much needed advance.
The timing gets taken out during accelaration because cylinder filling increases so a faster ignite happens as a result of the richer mixture.
From all the reading plus some testing I've done, I think the issue is that when hooked to manifold going from ported, idle timing goes up too high, so the distributor gets pulled back to end up at the same 12-14° idle timing when it was on ported, but now the vacuum is adding some of that idle timing. But that then limits the higher rpm timing because the mechanical is now down from 12-14, to probably 4 or so (rough numbers for illustration). So when acceleration is applied and vacuum drops, the mechanical is lower than it was when ported as the distributor was pulled back to compensate for the extra that manifold gave it at idle.
So if we go back and set timing with vacuum port plugged off, and set say 12° purely mechanical, then plug in manifold vacuum and timing goes up to say 25 (rough number)... Instead of pulling back the distributor, leave it, instead, lean out the idle mixture screws and turn out the idle speed screw. By lowering rpm in this way, it should reduce some of the mechanical advance. Or so goes the theory that David Vizzard puts forth.
Effectively, idle timing can be fine on ported but at cruise you want manifold advance to get that high timing number. That's the theory anyway
I think 🤔 the ported was a emissions thing i tried both on my 390 ford and on ported it ran good and the AFR was easy to get 14:1 especially on the Fwy only it woukd get hot 🔥 in stop and go idling traffic in the summer the exaust was 50 percent louder and at startup i would have water vapor coming out of the exaust . On manifold it was alot richer and i would need jet down a size or so alot harder to get perfect AFR usually be around 13:20 ish idling and 13:80 or so on the fwy but if was 50 percent quieter exaust and did not get really hot in traffic .
Alot of people say the factory never used full manifold ?. I think before 1975 they did on the valve cover it has a low initial timing like 6-8 degrees if it was ported it would or should say 14-16 degress ...
@@TheThirdWheel618 All of my older vehicles used full manifold vacuum advance except a 1973 Dodge Dart with a slant 6. Once I bypassed the OSAC valve and gave the vacuum advance can full manifold vacuum, the engine ran cooler and more efficient. Better MPG's, better drivability, better cold starts.
@@muziklvr7776
Yeah i think before 75 for sure it was all full manifold Ford had a valve that operated by engine temp you were on ported untill the engine reached a certain temp say 200 then it would shut the valve off and it would go to full manifold to cool the engine down ???? That says it all the factory knows they can reach better AFR with ported at idle but it creates a lean condition so they came up with the valve idea .
Thanks Uncle Tony! There are still a few us gearheads around that remember switching to ported vacuum after "desmogging" a 70s GM product. Power timing with a buddy!
Desmogging meant switching back to manifold vacuum
Well, we know the canister works. The distributor has to be curved to work on whichever port you use. If you take a stock distributor that was curved to run on ported and you put it on manifold you will have way too much timing. Likewise, if you plug a distributor into ported that was set up for manifold you won’t have enough. So there is truth in both camps on which is “better”. Best to know what you have for mechanical advance in your distributor and how many degrees at what vacuum your canister delivers to determine what will work for you. Excellent real world practical demonstration from Tony. You won’t get that anywhere else! 👍
I’ve been always using ported vacuum. I’ve had to listen to so many people telling me to run manifold vacuum, but I read something long ago about which port to use, and I’ve stuck with it! The only thing that I’ve done is try to limit the amount of advance, and keep my initial timing up. It’s worked so far, so good! 😉
Man, this is why you're a genius instructor! Who else would think to take a real distributor in the car to show what's happening?
Great video! I agree, ported, only, ever! I had a great Vocational Auto instructor. We had a Sun distributor machine. He taught me how to use it and to set up and recurve distributors. Must have done 100 over the years. I loved using that and a Sun engine scope, he also trained me on. Fun stuff. A lost art these days.
You got balls standing on the side of the road like that lol
I thought I was the only person crazy enough to tune the engine on the roadside....lol
Brian J. Medina your math is lacking skills
Meh. Been doing that for years
@@Welcometofacsistube holding a sign? Lol
@Curtis Fleabag I'll only do that with a homeless and hungry sign in my hand. Not a distributor lol
professor Tony's classroom! You really do love teaching!
Tony you are giving me flashbacks, its the mid 1960's auto shop at Martin VanBuren HS Queens. The vacuum gauge was our #1 go to diagnostic tool. Electronic test equipment was years away. I remember buying my first dwell meter and thinking how advanced things had gotten.
1960s car were always ported vacuum to the distributor. Late 70s 80s cars use manifold vacuum with the thermo switch between vacuum port and distributor. I believe some use both to the thermo vacuum tree and delay valves/check valves as this was to delay vacuum advance untell engine was at operating temperature and converter was hot for better emissions.Less timing equals more complete combustion and less oxides of nitrogen. I did state Emissions testing, tuning,rebuilding the computer control carburetors. Adjusing with old Catalytic converters on the vehicle or a cylinder with low compression in one cylinder this was challenging stuff at the time.
The ONLY difference between the two is you don't get vacuum advance at idle with ported vacuum. They both work exactly the same at part throttle and wide-open throttle. Use which ever one makes your engine run best.
It will let you know.
Works for me!!!
Nope. Watch a manifold and ported vacuum gauge side by side and you’ll see that they are not the same at, for example, low load/cruise conditions where the throttle is barely cracked and manifold vacuum is high. When you’re flying down the highway in cruise you need the timing only given to you by manifold vacuum advance. Better mileage and cooler temps.
@@yeboscrebo4451 Once that throttle is opened past idle, there is FULL vacuum.
I think its something that will be debated endlessly. The only way around it is to dyno two cars, one with a factory engine and the other with performance mods. Test both running both ported and manifold and see the power band differences. Love your videos. All the best from Oz
Or just take the same engine and tune for ported on the dyno then tune for manifold and see which one wins.
There would be zero difference on a Dyno. You don't leisurely cruise on a Dyno, you crack it wide open under a heavy load--- ported or direct manifold vacuum are BOTH going to give exactly zero added degrees vacuum advance, no partial throttle runs on a Dyno.
Glad I drive a truck and don't drive a dyno
@@hiswordheals9710 From what I've read, most modern vacuum advances will give you 12 to 14 advance and mechanical advances will give you 12 to 14. As the vacuum drops, the mechanical advance makes up for it depending on both timing curves. Some mechanical advance only distributors will go as high as 28 to 3,000 rpm or even higher, but mechanical advances are more typical of motors built for heavy load applications such as tall deck 366's or tall deck 427's (extra oil ring in the pistons to handle higher advance/compression/heat at higher RPM's under heavy load).
Some vacuum advances are also adjustable so we can play with the timing curve. We know that as RPM's increase, the vacuum increases even as your primary throttle plates open up but as your primary plates open up more than half way, the vacuum begins to drop.
I'm spitballing here, but I think the vacuum begins to drop as the primary throttle plates open up past half way but if your engine RPM's are in the high 2000's or higher the vacuum is still mostly maintained so it doesn't drop by much.
It's when the secondary 4 barrels (throttle plates) open up that the vacuum tends to crater. Your vacuum advance drops to zero on a SBC with your carb fully open up to around 4500 but then slowly picks up past 4500 advancing minimally by 4 degrees or so around 6500 RPM's. But then, if you are pushing a motor to these RPM's on a dyno, it's built for it. This isn't to say vacuum advances won't be used on the street pushing these revs, but the chances are more likely that a motor on a dyno pushing 6500 or higher is built to race with a lock out distributor with all of it's advance at startup.
The type and size of your carb also effects vacuums. A Rochester for example, has much larger secondary venturi and throttle bores than primaries so as your secondaries open up on a Rochester, the ported and manifold vacuums drop lower and more quickly than equal sized throttle bores. Same holds true for larger CFM carbs such as a 750 on a 350 sbc, the vacuum off your port will be lower on a 750 compared to say a 600 CFM carb because your venturi and throttle bores are larger on a 750.
Hi performance cams, ported heads and high rise intakes will also drop your vacuum (substantially), but that's for another conversation. 🙂
Uncle Tony, Thanks for tuning me up! It’s been a while since I’ve been in this deep. I’m doing a major rebuild on my ‘79 F100 (bought it new at age 19). Since most emissions parts are obsolete I’ve had to reimagine as best I can. OE vacuum diagrams showed the vacuum advance working off manifold vac, trying to set timing, adjust idle; and it wasn’t making any sense. I think I’ve got it now.
I owe you one, or more.
Again, late to this video viewing.
Lovin you classroom venue. Was a little worried, bout you being along side the highway with the kind of drivers out there these days.
Appreciate the effort, and you managed to show this very “thick headed” guy how this system works.
Thank you sir.
I thought I understood port vs manifold for distributors, but this made is so clear I won't ever forget
My car seems to idle better with the extra timing from manifold advance. It comes off when I hit the gas. So what? It goes back to where I set it in the first place. What am I missing here
You are not missing a thing, Tony is.
Sweet demo rig. I've never thought to try that. Really interesting to see a real world experiment. cheers Unc. My spare sbf points dizzy recently got rigged with a battery, coil and a plug, held to the workbench in the shed by a chunk of railroad track and spun up with a skateboard wheel with a silicone hose tyre mounted in the drill. Mission was to calibrate the new old been in bits custom tach. Works a treat. Dead nuts on to the digi timing light tach after tweaking it. Some people would have rigged up a signal generator circuit but analogue with dangerous fizzing taser sparks way more fun. Even the wife was impressed.
I changed the cam on my 350sbc and had left the vacuum at ported. It ran good set at timing and everything. I read up about how ported was made for pollution control and hindered car performance at idle. I changed it to manifold vacuum the other day and holy shi*!!! The car ran better, idled better, and drove well overall. I decided to play around with the timing a little and move my distributor a tad bit more with manifold vacuum and damn I got even more kick out of the mouse. Didn’t know how much performance I was leaving at the table with just one darn vacuum line.
This channel is a gold mine. I learn something every video. I always thought vacuum advance's were always connected to manifold until the early 70's when they switched it to ported because it allowed for better emissions. My understanding was that if I want better emissions I should do ported, but if I want better drive-ability I should do manifold.
Yes ported it runs hotter so it will burn off the fuel more although in stop and go traffic in the summer you can get into trouble running ported . I ran ported and I could get 14.7 or more on the AFR gauge idling on manifold I would stumble out past 12.9 or so less timing the leaner it is more timing the richer it is problem is the distributor is not tuned for manifold vacuum a adjustable pod is a must .
On my old Porsches I always ran mechanical advance but on my Thunderbirds I always stay manifold.
I thought I understood everything about vacuum advance. I never took a distributor in the cabin with me though. Once again UTG blows my mind. 🤯
The difference is absolutely not opposite. The only difference is you have no vac advance at idle. Off of idle it is the same. The question is what do you want at idle. And the answer is not the same and every condition.
I always learn something when I watch Uncle Tony. Hard learned knowledge that he's willing to share. Thank you for taking the time to teach and entertain.
If you didn't already know this, then you are not a hot rodder!!!
Good simple explanation. Using manifold vacuum you are defeating the whole purpose. I could do a whole video on this myself. I've read many of the comments here and many have no clue. Back in the day (maybe they still do) they had those Sun machines that you could fine tune a distributor. Change centrifigal springs if need be for certain RPM advance so no vacuum needed. A lot of people don't know that some vacuum advance cannisters are adjustable through the vacuum port with an allen wrench.
Excellent explanation. Most people overcomplicate these things because they don't understand fully what they are talking about. The simplicity of this demo speaks for itself
The demo is TOO simple. He showed what happens to the dizzy when the advance canister is hooked up to ported or manifold. He didn’t adequately explain why you need different timing at different levels of load or rpm. For a more comprehensive demonstration, the dizzy needs to not be removed from its symbiosis with the other parts of the engine. A better approach would be to show two different vacuum gauges one from ported and one from manifold at the same time. Then, take the engine through different circumstances in load and rpm to show what is happening with the timing. Uncle tony was able to explain the opposite of the truth because his demo was overly simplistic.
You explain everything so well but there's always someone who wants to disagree with what you have to say, which is from many years of experience. Most of them probably never even turned a wrench!
Thank you Professor Tony! 😎
Something that helped me as a kid was to think of it as "negative pressure" instead of vacuum, then sea level pressure after opening the throttle.
Is this backward for just me or a bunch of people? I thought manifold vac was better for big cam engines to help smooth out idle. To date everything I have read has always said manifold vac advance is the way and that ported was only good for some mopars and later used as a crutch for the gas crunch smog era emissions. Great video as always demo is excellent. Maybe I need to go flip some hoses around and save some at the pump due to more mpg. Thanks for the knowledge!!
68 440 magnum. Original Carter 4429 only had one port available (other than the choke pulloff) and that was for ported vac advance.
There will be spring or weight differences on a stock distributor, depending on whether they want to emphasize street performance, track performance, economy, or emissions. You can alter those goals by changing total vacuum (different can or link), and/or by changing the centrifugal springs or limiting the travel of the weights (more difficult).
Just remember if you limit vacuum advance or weight travel, you may need to alter idle timing to ensure higher rpm advance while cruising is not way off.
You might also find a deceleration solenoid (or vacuum device) that prevents the throttle from slamming shut and sending manifold vac to over 25, causing timing to advance when it would drive emissions highest (you're not interested in performance when decelerating anyway but Uncle Sam is particularly interested in emissions at that moment). Salute that solenoid, it's a good soldier.
But when you are part-throttle accelerating your 70's Dodge and interested in performance for a few seconds, there's a traitor called the OSAC Valve (usually hanging off the air cleaner body) interrupting the vacuum hose from the carb to the distributor. That thing prevents vacuum advance for several seconds while accelerating, and since you just left the stop sign, your revs are not high enough to give centrifugal advance, so with timing delayed you end up pushing the pedal way down to keep up with the 60's car beside you (no OSAC delay). Sound familiar? Bypass that OSAC, plumb the vacuum direct to the distributor.
Off idle response and cooler running engine have nothing to do with performance? Don’t think so. There is a lot going on with a mechanical distributor, springs and weights, mechanical advance degrees, vacuum advance degrees, response adjustable and non adjustable vacuum cans. Most people don’t have the time or energy to dial in and tune a mechanical distributor let another understand how it all works together. It’s hard to explain, I have tried every which way with my olds 350 and 350 sbc, hands down manifold for me.
I'm a huge fan of manifold vacuum and I can see many benefits on my 41 Chevy inline 6, since I swapped it over to manifold. Especially mileage and temperature. What a lot of folks saying : ported came with emission in the 60s is a myth though - my 41 had ported from the factory, some cars even earlier - why? I don't know, since the engineers back than must had have something in mind - but that would be an other interesting discussion.
Sorry. Ported vacuum is for smoggers. At idle and low throttle the mixture is lean and needs advance. Smog distributer curves had tons of advance, like 12*, at idle to compensate somewhat for the ported vacuum advance. They did this to make the car run hotter. My 68 L36 Corvette used 4* initial and full manifold vacuum to the cannister.
Correct. The ported vac would be exactly the same as manifold vac anytime off idle. So manifold vac would allow more advance at idle and for longer burn times needed at idle. Plus low base timing for ease of start before building vac
That’s the best example of how it works I’ve seen! Thanks for the video I’ve been hooking it up wrong for years now!
This confuses me. Wouldn’t you want timing advance at high vacuum/low throttle situations? There is almost no port vacuum when the throttle is at or near idle.
Yep. Tony’s wrong
ABSOLUTELY!!! Anyone that doesn’t understand this doesn’t understand ICE’s!
Basic. Ported. Manifold give an unstable. Step on the gas and timing drops out. Big cam, put it in gear, vac drops out. Idle.surge.on cam at idle, timing drops out, wants to stall. Manifold is not what you want.
What does fry burger think?
Yep, mostly mechanical can be good too, especially if it's a race car or constant heavy load too, where there's not much vacuum signal. A vacuum can that comes in fast with not much vacuum doesn't drop out as quick, or only drops out just a small amount (mechanically limited) might be fine running on manifold vacuum. GM for instance probably used near 30 different vacuum canisters on the many applications, both manifold and ported were used. Later vehicles with emissions were mostly ported and earlier, especially performance, were manifold. General vanilla in 70's ported was quite common.
Dont you guys realize its the same thing as soon as you step on the gas there is zero difference between port and manifold, port vs manifold affects idle only
@@researchandbuild1751 well hello again! Yes you are correct, ported and manifold vacuum are practically identical once off idle.
@@researchandbuild1751 If your can never moves, or moves full advance, there's a difference. For instance, a can that's calbrated for all-in @ 18" will likely produce a different result than a can that's all-in @ 8" vacuum, right?
sometimes i like to use manifold vaccum with a cammed engine. it tends to keep the fenders from shaking off it but usually i just end up not useing the vac advance.
True and probably helps the spark plugs at idle
Yeah I put a cam with a tight lobe separation angle in the my truck it isles so much better on manifold
@@tl5108 Tune your shit right.
If it runs better on manifold vacuum wouldnt you adjust initial timing?
@@boss351gt6 well running it on manifold vac just makes it run smoother the when you stab it. vac drops n you revert to mechainical advance. only really food for cruising n idle
I've played the ported / manifold vac game before. In the end both of my cars are still on ported. With a properly set up dist., initial and total dialed in, ported is where it's at. Much smoother part throttle acceleration.
Part throttle acceleration is the domain of initial/mechanical but mostly mechanical advance. Ported timing is redundant in this regard - it’s doing the same job as mechanical timing just a more limited range. Use manifold advance and you free up the vacuum canister to do a different job that ported is unable to do - advance timing at high vacuum/low load situations.
Sorry Tom, I couldn't see ANYTHING moving in the distributor at all. As a side note, I love your channel & your old school style & have learned a great many things from you in the past. Thank you Tom. Len from Canada.
Why not let the weights do the advancing and keep the manifold vacuum advance for the best idle and light throttle cruising?
Great work as always Tony, clear and concise answers and demonstrations that clear the air and give actual information that is physical and tangible for everyone to see and more easily understand the concept. Nicely done sir
on a stock distributor....you are not wrong, sir. really appreciate the demonstration and posted content! explained very well, and clearly.
Not totally correct there sir. When base timing is set properly, you need to have the vacuum line disconnected and plugged. Then once it's set, you can plug back in the vacuum line to your distributor. With it connected to full manifold vacuum, You will have a lot more advance at idle. Some motors like this setup. The motor will run cooler and not as lean. You will have to adjust your idle screws down which is a benifit in some cases as now your motor is less likely to diesel when shut off. Also your idle mixture screws will be more functional if they weren't before. Once you began accelerating the amount vaccum advance will drop some as in your video due to less vaccum in the intake manifold from throttle plates opening. Except it will still be the same actual amount of advance as if you had it connected to ported vacuum. The ported provides no advance at idle so the motor runs hot, and lean. It will make cleaner emissions this way. When you accelerate the ported timing port then applies vacuum to the distributor and advances the timing at that time, but it's to the same amount it would be if it was connected to straight manifold vacuum. The amount of vacuum advance does not change depending on rather it's hooked up to full manifold vacuum, or ported. The only difference is full manifold vaccum will give you more of that advance while at idle, where ported waits until part throttle. Both will have the same timing at part throttle cruising and WOT.
Thanks Tony Best explanation. I am a visual type of leaner not reading a book or explaining the function and not showing how this function actually works while in use.
76 vette came with 6 BTDC, Vac Adv to Manifold. If sVac. Adv. is switched to ported, vehicle will overheat at idle, running soley on initial 6 BTDC.
Vac Adv. dies off at throttle but timing springs/weights compensate for the draw down. This cannot be seen in your example as the distributor is not rotating.
When throttle is close to a cruise, initial timing,vac adv. timing, and spring timing are all incorporated for better fuel economy.
One advantage to using timed vacuum advance is that an engine with conservative ignition timing, has better engine braking than one with generous ignition timing. Nice thing to have in hilly areas!
It really takes a really knowledgeable and has some common sense mechanic to dumb this stuff down to this level. I admire your patience with the keyboard warriors.
No it takes a really dumbass to complicate it in their head more than it really is! If you need it dumbed down to grasp it!!
Uncle tony I love your videos. Hi from Australia. I feel if people are not up to speed with basic things like vacuum advance, Mabey they should choose a new hobby. But then I remembered we all have to start somewhere. So. For the young blokes who watched this I thank you. You will teach them
An hei or gm distributor would have been a bit easier to actually see what's happening there but you sir are 100%spot on
Thank you for all the great info and breaking everything down step by step, and for free to everyone who wants to learn the right way and understand how and why for every video you make. Thank you
So doing a lot of reading on this subject. With leaner mixtures you want more advance for a full burn. And as the mixture richness increases you want the timing retarded since the higher cylinder pressure doesn't require as much time to burn as a lean mixture. So wouldn't that mean the most efficient burn is happening with manifold as ported is making for a less efficient burn and higher exhaust temps? Which is putting more stress on the motor with more heat?
I have certainly seen both sides pointed out. However doesn't this demonstration just show Vacuum Advance going away as the vehicle is accelerated. You would still be left with the same amount of Initial+Mechanical. Does that extra advance dropping out quickly cause a negative performance issue and is there MPG benefit to having that extra timing during idle?
Man wish I had know this some 30 years ago. Completely understand the difference between ported and manifold vacuum. Now that explains why it never ran as good as it should have.
This is very good. The vacuum system is overlooked by many and understand by a few people. Remember, your knowledge is not the same that other people have or think they know.. People start off wrong and the stay wrong. It takes some person like you ( Has credibility) to head people in the right direction. Thanks again
So at light cruise in hunts for the highest manifold vacuum and allows for the best fuel economy. At high-altitude we add a few degrees of base timing and move the vacuum advance to ported. This allows for a smoother idle and leams the carburetor out by raising manifold vacuum and allowing the power valve to pull slower. There is also a third vacuum source called the venatori vacuum. This vacuum source is used only to control EGR through Chrysler's famous EGR amplifier mounted on the firewall.
I've was taught to do my timing with the vacuum advanced off and then attach the line to the port on the base of the carburetor, never thought that much of which side to have the distributor to get its vacuum from, I've always put the line to the carburetor ports, if on the manifold vacuum tree then cap it and place it to the carburetor.
Hello Uncle Tony,
Thank you very much for all the information you have given us. 1st Oct, 2019 I bought a 65 Mustang that needed everything so I could learn about these things we drive every day. RUclips and manuals have taught me much but there are things that slip through the cracks here and there that I have to catch as aside note in some video about something completely unrelated.
Then I found your channel. Your so direct and actually bother to put into video format your advice and knowledge. I understand how actually bothering to set up, film, edit, and post is a time-consuming process. So again, I thank you for taking the time to put your experience into RUclips so green mechanics like myself can learn.
I have a small request and if a video has already been made then please if anyone could point me in the right direction I would be most gracious. You had spoken briefly about how your lifestyle is in your cars. Specifically, you don't keep cars with really high-end paint jobs because of the upkeep a super high close finish requires. I have been trying to discern what you do to paint your cars by looking at your cars in your videos. What do you recommend as a paint job for a daily driver classic?
So far I have done all the prep work, then primer, blocked it, then base coat, and blocked, then matte clear with hardener. What would be the simpler way for daily driver upkeep?
Thank you again for everything.
Tony give those hood hinges a little wd40 🤣🤣
Friends 350 Nova, when he changed manifold and carb ran tired. After talking he showed me how the install info said to use manifold. I switched it to Venturi and after having to replace the vacuum advance unit car ran great. Manifold vacuum had separated the diaphragm. Never did use manifold on anything but the wipers and heater switch
I'm confused. You demonstrated what happens when you get ON the throttle on manifold, but then demonstrated when you get OFF the throttle on ported. what does ported do when you get ON the throttle that makes it better?
The one area I still struggle with is why to use port vacuum, like Tony suggests, when the distributor weights and springs were designed to advance the timing mechanically under throttle? Why would the car manufactures design both types (mechanical and port) to advance the timing when one can do it by itself. The explanation on using manifold vacuum makes more sense to me because under cruising (part throttle), the air fuel mixture, which is less dense, needs more advance timing to allow the mix to burn efficiently, making the car run cooler and smoother. Advancing the timing under this driving condition can only be achieved through manifold vacuum. So, the system uses manifold vacuum at idle to low speeds then switches to mechanical advance when under acceleration, keeping correct timing under all driving conditions, thereby negating the need for port vacuum all together.
Exactly my experience, I can see many benefits of manifold vac on my inline 6 (261) especially temperature, starting and mileage.
Exactly. Ported timing is redundant. Its performing the same function as mechanical just laid over the top of it. Manifold advance gives you what ported can’t - timing in conditions of high vacuum/low load when your engine needs it. Uncle Tony has this crusty old idea lodged in his brain and doesn’t revisit or question the old beliefs he’s been harboring for decades. Classic old person.
Nice demo Tony!!! I too had questions and that makes it pretty clear.
Of course now I'm contemplating hooking up some kind of valve to both ported and manifold vacuum with some sort of cable or solenoid to switch between the two. :)
@Jonny longfella Cause it'd be possible? :)
You can't teach an old dog new tricks. Once their new tricks get old? You can't teach them anything! You do what you do Uncle Tony! Simple as that!
Should be added that some advance canisters can be adjusted with a tiny hex wrench up the vac tube to adjust how much timing the canister gives. Aftermarket "performance" canisters typically have this feature.
Yes , I bought an adjustable vacuum advance for my 75 Caddy and kept a little allen wrench available so I could adjust my vacuum advance at Cruise or if I was Towing a very heavy load with 87 octane . I recurved the distributor timing with different springs and different factory GM weights in addition to the adjustable vacuum advance. I think the vacuum canisters that have the hexagonal instead of the round bodies have a plate in there that the adjustment screw goes through and that screw can give more or less pressure on the spring that the vacuum diaphragm pulls against- I'm not sure if the round ones are adjustable or not. My buddy bought a Mopar electronic ignition conversion kit for his 69 roadrunner and I remember the instructions were pretty cool and thorough and how to setup the vacuum and mechanical advance for performance and mileage. I think going back twenty years ago it said to set up the mechanical advance first (with the vacuum advance disconnected) by doing I think it was second gear acceleration runs to optimize performance without pinging or detonation . And then after you had the mechanical advance optimized you would hook up the vacuum advance and adjust that for driveability and mileage.
I disagree. You want the vacuum advance at idle and part throttle cruising; however, you want it to drop off under full throttle acceleration to prevent detonation. One reason why you want it at idle is so you don't need as much base timing (around 10° or so) for easier starts, but still hit around 26° or so at idle after it starts, allowing it to idle much better. The vacuum advance is for fuel economy at idle and crusing, as well as for easier starts by allowing the base timing to be set lower. The vacuum advance should have no bearing on total timing at full throttle, high load, low vacuum conditions. With base timing + mechanical advance, you should have enough timing for full throttle acceleration just before pre-ignition, independent of vacuum advance. At cruising, you want much more timing when the load on the engine is low and the risk of pre-ignition is pretty much non-existant; hence, base+mechanical+vacuum cruising you should see about 54° or so, but only about 36° give or take at full throttle, high load conditions, where the risk of pre-ignition is high (which is why you want it to drop off, not come in). When using the timed port, you're not seeing any of the idle benefits you could be, and your base timing has to be set higher to get a good idle, making it harder to start. Original vacuum advance setups were on full manifold vacuum from the factory up until sometime in the early 70s I believe, when emissions regulations began to have much more bearing. I'm not sure what the thinking was behind the change, I just know there was a change. But just running on base timing doesn't give the engine the amount it wants at idle; where again, the risk of pre-ignition is pretty much non-existant provided the carb is tuned correctly for the right amount of advance at idle. You can see numbers and management philosophies like these when looking at ignition tables for fuel injected engines; even on my '98 vortec 350 (just a gen1 small block,) the stock ignition mapping is like this.
Great demonstration. You do a great job of explaining stuff in a way anyone can understand. Good teacher.
Holy shit, what a great demo! I’m glad you didn’t throw the dizzy like it was just a carb
Hi uncle tony, very good video I’am learning how to set up a engine your way . I’m self taught working on cars for along time I don’t know everything I wish I did at 71 years old just keeping at it I like working on cars thank you for all your help 👍🚘🔧
In my personal experience, I m never able to get full advance at low speeds with ported vacuum. Throttle angle is too low to uncover the port.
Tony, love your channel. I’ve got a 70 GTX with a 440. The bottom end is stock, the top end, I added trick flow power port 240 heads, and Edelbrock performer RPM intake, an Edelbrock performer 800 CFM carb, a Comp cams 491 lift hydrologic flat tappet cam, 236 duration @50, Howard’s lifters, TTI 1 7/8 headers and 3 inch exhaust. I built it to be a fun dependable cruiser. The car had points ignition before I pulled the top end apart. The engine was completely rebuilt 2,000 miles ago btw.... I bought a summit electronic conversion ignition kit. I started the car and I couldn’t get it to idle, it’s an automatic and when I put it in gear, it died, or was terrible. I bought a JEGS distributor and their ignition box, better but not good. I sent in the summit distributor to have it put on a sub machine by a guy in Ohio. He asked for my cam and gears and compression (10.5:1) ratio. He promised the world, well, it made it worse. Wouldn’t rev over 3,000 rpm. Oh, on the manifold side, it’s pulling 13 inches of vacuum at idle but on the port side, it’s pulling 5 inches. That doesn’t seem right. I heard about FBO ignition. Don said his system runs off the manifold side. I installed his system, it’s much better but but when I connect the vacuum to the carb, it starts popping through the exhaust like crazy. When I run it without the advance hooked up, it’s pretty good but still not perfect. I’ve been watching your channel for awhile now. You’ve forgotten more than I know and I’m pretty good with mopars. I would really love your take on this. Thanks Uncle Tony!!!!!
It’s your carb. Or something with your idle speed screw. You should not get ANY vacuum of your ported side of your carb. It should be at 0. If you can’t get it to idle it sounds like your initial timing is off. Quick way to find out if it’s off is to plug your distributor to manifold. If it idles better then yes your initial is off. Manifold adds timing at idle so that’s one way to see if that’s your problem.
Its more complicated. It really depends on how it was setup from factory. For example. if distributor does not have mechanical advance, than using ported vacuum advance is how its done. Also how it vacuum advances different on different era distributors.
What I found with my car is that it required less throttle opening to maintain a good idle with manifold vacuum. With ported, I had to have the throttle open more, no big deal, except that the car tended to run on and diesel when I shut it off.
Your results may vary.
Sounds like you are not tuning your carburetor correct. To lower your idle speed, you need more air to bypass the throttle blades. Opening the secondary blades a slight amount, or drilling the primary blades. The idle circuit alone, may not supply enough air for a good running idle. The added air will allow you to close the primary blades and the idle circuit will function properly. Please read HP books Holley carburetor manual. Your welcome.....
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Thats a Chevy Engine you are working on 😅😅😅😅
Perfect explanation with a demonstration to help us visual learners!
I gotta admit, my pathetic eyes barely registered the movement. But what a great way to demonstrate what the advance is doing!
Well on my 70 Buick Lesabre with 350, I swapped the vac hoses around on my thermal vacuum switch. I saw I was running full manifold vac on the dist. The bottom port on the drivers side on my quadrajet had no vac unless I worked the throttle. So I mistakenly criss crossed them. When I made the switch, it was a much smoother ride and swifter kick in the pants when accelerating. When the car is idling hot during heavy traffic, the tvs plunger is supposed to shoot up and block off the ported and allow manifold to help cool off the engine with higher rpm... I realized something was wrong when my engine really bogged down when it got over 190 deg. But now, my engine runs much cooler.
I remember the old Autolite dual point distributors on hi performance Chrysler products did not have a vacuum advance.
Thanks Tony.