Street gearing and an automatic trans with a near stock converter: Vacuum secondaries. Everything else, double pumpers. I've been building carbs for 40 years.
What cracks me up is my buddies and me figured most of all this stuff , you guys talk about and test on all your shows. In the late 60s early 70s. All of use trying different things the hard way , racing each other, one step at a time. the drag strip times was our dynamometer. Really miss those times,we still talk about them, those of us still alive😢
Back when parts were cheaper inflation wasn't so high, you could pick up parts just to test them on your own.. A Holley now is most of your house payment lol
What cracks me up is that people are *still* talking about peak power while completely ignoring drive-ability. Peak power is fine on a dedicated drag car but it doesn't matter very much at all on the street.
The dyno numbers are impressive, but it really comes down to seat of the pants results. In my 69 big block Chevelle, vacuum secondaries with a 4-speed and 3.73 gears always gave me steady consistent launches. Switching to a double pumper carb, I only got good throttle response when I switched to a 4.56 rear gear. On the street, the launch was everything! Stop light to stop light never allows you to reach the upper power band. Street tires and the street itself were always the limiting factors as well as local law enforcement.
Great information. I had those same questions and, I agree with your answers! The only other difference that you qualified in the beginning is, that (I.e.)a 750 carburetor would be the Minimum that carburetor would flow. It could actually flow much more in a given throttle body. Great job gentleman!!
Three Holley twos on a 428cj falcon was my money maker. With a 300 degree hydraulic cam it was capable of 7500 rpm. That was in 1972. The hottest setup for the street was the 406 3x2 induction for the FE engine.
@@KingJT80 Yes, I was expecting them to say that the HP difference was related to A/F ratio differences but that did not happen. They showed there was no difference in actual airflow, so I was left wondering what was the real reason for the significant HP difference.
It would seem to stand to reason that if the airflow is the same and the fuel flow is different between carbs, the air/fuel ratio is going to be different. Which begs the question of how much and how much difference the different ratio makes. It's a really odd thing to completely ignore in the video.
My thoughts exactly. Air probably had higher velocity before entering the dp carb than it did with the vacuum secondary carb without the air hat. Like the old school velocity stacks, or Weber 8 stack system.
I built street/strip 440 my 66 Belvedere. Had 700 double pumper. I tweaked rebuild thermoquad 850. Boy did that thing run!! Never a hickup or stumble or anything. Ran flawless. Snappy throttle response and would keep pulling hard!! Im a thermoquad believer fanboy totally!
its not enough deference in power to make it worthwhile, I ran a vacuum 780 cfm on a super comp dragster 355 ci with horn still in place worked great interesting listening to it coming up on the brake. what shows up on the dyno is not always track information. thank you love the videos.
that 491 vs 514 is basically you saying you have a 500 HP small block as opposed to to saying yeah it makes almost 500 thats kinda a big difference. if i ran a mechanical secondary on the street (which i might still do) id run a choke. that i do agree theres no real difference vs running a true chokeless race carb even if it's the summer. 780cfm on 355 inches can and should run over 7000 RPM
23 PEAK HP difference on this test is almost a 5% increase, & the double pumper made more torque & HP from just below the test starting RPM all the way to max RPM. That's a pretty substantial difference. Double pumpers have zero disadvantage, "when properly tuned". I've always run them, since 1971 & never had a problem, even in cold weather, without having or using a choke. My current 750 Street HP on an Edelbrock Air-Gap intake & NO heat riser fires up & immediately idles in summer, takes a couple starts & hold the throttle slightly open in the winter, until the engine builds a little heat. My 500HP, 409ci SBC also gets better fuel economy than my computer controlled FI 2004 Tahoe. But, I will add that I've been tuning carbs for over 50 years & learned some big lessons in the early 80s working on highly tuneable Weber carbs, which the Holley HP series tuning is comparable to with their "air correction" jets!
@@SOLDOZER If you think 5%, or 23 HP isn't noticeable in the vehicle & going down the track, you're very naive or have never raced. Pro Stock guys will spend $10,000 to find 1 or 2 HP with a motor that's already making 1,500 HP! 5% is a BIG pickup! BTW, our ALL MOTOR door slammer has gone 7.97/168 on race gas with 4,000 foot altitude air density, that's 7.70s/172 with 70* sea level air! How's your slug run?
I use a Quickfuel brawler 850 DP.on my Mopar 500 inch low deck with ported heads...it's also equipped with a ed's Victor single plane intake. I think this setup is bait for a dual feed carb! A vac sec carb can work it's just doesn't have the fuel curve of the DP...also Thompson perf atomizer plates on both ends of the dual feed carb really help in low end torque
I have a mild 318 in my Chrysler. Stock heads. 1980 model. It has a mild comp cam 268 h and edelbrock performer intake with an eddy 500 avs carby. Hei ignition with extractors and a full 2.5inch exhaust. Stall converter is a 2300 and diff ratio is 3:45 lsd truetrack. I removed the choke butterfly from the front of the carby as this was a restriction and it certainly did make a difference on how it performs. Runs real well. Starts fine with no choke,just got to feather the throttle for maybe 30 seconds then it will idle happily. On the dyno as I had carby professionally tuned,it made 220hp at the tyres. Not massive but very good for what it is. I often wonder how it would change if I was to go for a bigger carby? Like a 650 perhaps? But they cost a lot so I won’t worry about it. Great video by the way 🤘
would you not test the vacuum secondary with the secondaries jetted up? the hypothesis being that it should then match the fuel delivery of the mechanical secondary. maybe this way you get the better of both worlds?
Right...Like was mentioned the air velocity draws fuel from the accelerator pump discharge nozzles / circuit once the throttle blades are fully opened. They continue to flow fuel. I have seen that occurring on camera footage before of carburetors running on a dyno. One of these days i'm going to mount my go pro under my hood to see what goes on. I've spent a lot of time tuning my junk using both vacuum secondary and double pumper carburetors. Story. One tuning session after I put my AFR gauge in the car I was working with different power valves. Changing different ones in and out for hours. Driving and observing. Nothing was effecting the readings. I took off the front bowl and metering block again...I was starring at the metering block. Looking at it in disbelief. Just starring for like five minutes. When I saw what the problem was. Holley did not drill the power valve channel restriction holes in the metering block ! DUH !
There was one I'd like to see in addition to this - that is how much bigger do you have to go in vac secondary carb size to negate the double pumper advantage?
@@ThePaulv12 maybe instead of relying on free entertainment to do it for you, you should do the test yourself and then enlighten everyone else for free
These are thing I struggled with early on. Eventually I ran Choke carb tuned for winter. Then a different choke horn delete (sawed off and polished away) carb tuned for summer. This was before you could get a "race" carb with that done already. The double pumper horn delete was for summer. Vac sec for winter. They ran the same in the environments they were tuned for. Nobody knew.
I had a 62 nova straight 6 that in winter or summer pump twice and she'd start and idle no chock. With engine hot just turn the key. That car would idle all day and not skip a beat, smoothest carbureted vehicle I've ever had.
Could the fuel difference not be that the spring in the vacuum secondary carburetor is too stiff and if you installed a lighter spring the secondary would open quicker and be closer in power to the mechanical secondary?
You guys could've just made a phone call to AED Performance in Richmond VA and they could've saved you alot of time and explained the difference to you and how and why one would make more power over the other per application. Those guys are very knowledgeable and have been doing this stuff for many years
If the double pumper is adding more fuel (via siphoning through the a/p discharge nozzles) to the same air volume, the mixture is richer. Why not enlarge either the main jets or the power valve restriction in the vacuum secondary carb to achieve the same fuel/air ratio?
While that would have been worth testing, it seems their criteria at the onset was to test apples to apples from the factory instead of fiddling with them whatsoever. I bet you could compensate a bit for what the vacuum one lacks in and probably pretty easily so it’s disappointing they didn’t test for that.
The problem is distribution in the Vacuum Carb vs the DP. It's more than just the volume of fuel added by the siphoning. It's also distribution. You've got 4 separate barrels in both carbs. All the same size and physically in the same spot geographically speaking on the manifold to which they are bolted. This is where the similarity ends though. While air flow is the same in both the ability to atomize and mix fuel is different. ALL THE FUEL supplied in the two primary barrels of the Vac Carb must mix with air supplied by all 4 individual barrels of the carb. The front two will supply a little bit richer mix to the cylinders supplied most by the air coming from the front of the carb and the cylinders mostly supplied by the rear bowls will be just a tad leaner. It's a trade off you accept for the drivability on the street. The mechanical carb supplies fuel to each of all 4 barrels and this no doubt gets you a much more even distribution of air and fuel both to every cylinder.....while not perfectly even you can bet it's far closer to even than the Vacuum carb will ever be capable of. As Steve B points out: you could richen up the primary circuit of the Vac carb but you'd lose all you drivability in the attempt and it still wouldn't work as well because while you may actually resolve "lean" in some cylinders it'll almost for sure enrich, past ideal, in those that were properly supplied before you richened up the primaries. Bottom line: This is why computer controlled injectors above each cylinder are how it's done on modern engines. With a Carb you can't have both. You gotta pick. Street or Strip one carb is going to be vastly superior to the other depending on your priorities. The vac carb can't match the WOT performance of the Mechanical and of the flip side the Mechanical will never be able to match the street manners of the Vacuum Carb. You gotta know which is more important to you ahead of time.
For me, in Colorado, we need choke just nature of the beast. Anyway I firmly believe dbl dumper on the track, spread bore on the street. A vacuum secondary just works better in stop and go driving.
QUESTION ... between the vacuum and mechanical carbs you measured the air volume to be exactly the same and measured the fuel flow to be dramatically different ... especially on the secondary side. You put the difference in fuel delivery down to siphoning fuel thru the discharge nozzle .... which is fine. But given that the volume of fuel ingested looks to be around 20+% LESS at some points, surely this would show up a lean condition in air/fuel ratio ??? So why can't this be tuned out of the vacuum carb ???
No. Both carbs would be providing the same air/fuel ratio and adding more fuel to either would just cause an over rich mixture ratio and possibly lose power. The DP carb is pro-active in that it squirts the required amount of fuel into the incoming air ahead of the curve which is why it allows better performance to begin with. The air and fuel enter instantly and are predetermined by tuning. No restriction equals maximum air/fuel inducted into the engine. The vacuum secondary design is a reactive design that restricts the airflow to an always less than maximum so that it can use the throttled engine pressure differential to initiate and maintain fuel flow to match the airflow. This can give good torque and is easier to tune to prevent "bogging" but it comes at the cost of limiting the engine to always less than maximum induction for any given load and RPM condition.
This. The primaries are working a lot harder/likely not metering as well as the secondary in the vac carb. I am guessing proper jetting would even these carbs up but ultimately the DP would be making more horses. Have a look at the secondary butterflies on a dyno engine you will see how they open/close depending upon vacuum and the diaphragm/spring setup.
Need to compare manifold vacuum for each run. My guess is that the more restrictive carburetor versions will flow the same amount of air, but at slightly higher vacuum. That higher vacuum would sap some of the potential horsepower.
When I was a kid ,dad pulled the choke blades out of some carbie he had on a 350 Chev.ever since then iv pulled out choke blades on single barrel strombergs,twin barrel webers and on and on until I figured out how to zip tie Rochester primary to the secondaries links all barrels at once lol .Now im tuning Nissan RB motors with a lap top here in New Zealand
I had a brand new 3310 vacuum secondary on my mild 383 right up until some chassis dyno time. The shop had a used 650 dbl pumper on the wall and after throwing it on the car I promptly bought it. WAY more stable AFR from the 3310 and I had all the springs and quick change kit. And this was a 3.08 geared, auto, mid 14 sec car.
Dyno "tuning" is a waste of time & $$$$ because there is nothing about the climate conditions or loading on a dyno that actually simulates real world street or track driving. NASCAR engine builders look more a the time it takes to accelerate the engine from bottom "track" RPM to peak RPM rather than peak HP with the load being the simulated vehicle weight & overall gear ratio.
@@bradgriffith4231 guess you ignored the part about AFR jumping all over the place. AFR is AFR. Everything you said may be true but gauge readings are true as well when used comparatively. Clearly one carb was consistent with fuel delivery and one wasn't. Nothing but truth in that observation.
@@madrew2003 Maybe y'all ought to learn how to properly tune a carb if your AFRs were constantly changing. Regardless, dyno tuning is a waste of time & $$$$ because there's nothing a dyno does that remotely resembles real world applications, whether on the street or track. Pro Systems will build & correctly calibrate a carb to perfection & ya won't even have to touch the A/F mixture screws or curb idle speed without even seeing the car, IF ya tell them the truth about your engine specs, vehicle, & altitude where it's normally raced.
@@bradgriffith4231 you sure do like to beat that drum, don't ya? Give it a rest. I use a wideband gauge to tune my carb and the trap speed at the track. Does that make you any less cranky?
I´d like ro know if the AFR was the same. If it´s "leaking" through the acc pump but the airflow is the same the dp should be a bit richer, meaning the jetting the vacuum carb should put out the same power. Yes?
AND it only makes sense to me that purposely enriched mixture through a metering circuit designed for the job and dispersed through the booster to atomize correctly would be better and more consistent than fuel "accidentally" admitted into the airstream through the accelerator pump squirter😵💫
First, your shows are so therapeutic! Thanks! Anyway, was wondering how much of a difference a drop-base air cleaner would have made in these tests...especially with the choke horn?!
Yes, which is more critical? To have a less than optimum intake manifold that fits comfortably under the hood topped with a free flowing air cleaner, or to have a tall, high flowing manifold that requires a low profile air cleaner and especially when used with a choke tower equipped carb? Years ago it wasn't a hard decision to install a scoop or change the hood on our cars, but today a factory appearing classic is very desireable.
The VS Brawler needs a “White” secondary actuation spring in the pod. Also the brawler should be tuned via jetting and air bleeds to compete more accurately/similarly. So this test needs to be clarified “Out of the Box” comparison only.
hey you 2 , how about a dyno run utilizing a correctly cfm rated carb with the exactly correctly rated primary and seconday jets on a 2 barrel then 4 barrel carb
I'd like to see you guys run tests on different types of air cleaners. Like an open top element, an old paper enclosed stock style, a velocity stack style element and a forced induction carb hat.
I have a Chevy 350 two bolt main. Headers and bored over 30.. what would be the best carburetor for this combination? Street car.. but I want a lot of torque and horsepower.
I daily drove a 650 double pumper for a year and a half with the choke horns milled off and it never once gave me a problem as long as I drove it at least every other day even in the winter. I highly prefer how they drive with a manual over a vacuum secondary, but that’s my preference.
have u ever ported the cam bearings to get a bigger cam in a sbc or season a block or polished the inside of the block for faster oil drop or put over sized cylinders in a sbc or use aluminum titanium alloy rods or balance all the parts rods pistons so on then balance the piston and rods to the counter weights then balance the crank with fly wheel and balancer. u guys should try this it will do insane rpms if u try this port all the ports oil water so on then port the heads open up the intake ports and match the new intake ports to the heads but u will need to go bigger on the cam so u will have to go over sized bearing on the cam when we did it back in eary 90's the custom roller cam just the cam was over 1000 bucks and u will need titanium locks on the valves. we did this to a 327 i helped but bell blue printed and built the engine he also went with tunnel ram with 13.5 to 1 compression for pump gas only 92
The difference from the vacuum secondary also is no back metering block and the four corner idle. Metering block possibly adding more fuel for the secondary system??
I run a Holley 670 avenger on my 428 C.I. Mild cam street Engine. It works perfect for me. A Holley Avenger Carburetor is a type of performance carburetor that is designed for street and off-road use. It is not a double pumper, which is a term used for Holley carburetors that have two accelerator pumps. A double pumper carburetor is more suited for racing applications, while an avenger carburetor is more user-friendly and adaptable to different driving conditions. Most people are non racers.
Aside from maybe being a bit on the small size for your engine, it CAN be tuned for serious performance and still get decent fuel economy. From my experience with the Street Avenger, the idle system is calibrated on the lean side which is fine(and desireable) for a mild engine and highly advised to use a choke for cold start & idle. When you start adding a cam and a bigger manifold- especially an unheated one, the idle system calibration will likely be too lean and not only will it be difficult to achieve a good idle but will also be difficult to eliminate an off idle stumble and stomp on the pedal pop through the carb. The fix would be to open up the idle feed restrictions in the metering block a few thousandths of an inch such as going from .028" to .031". If your idle mixture screws need to be turned out as much as 2 turns, performance would probably benefit by increasing the idle feed restrictions by a couple thousandths. I like to shoot for 1-1/2 turns out. Often when a performance carb is put on a mild engine, the mixture screws require less than a turn out for best results. That carburetor will most likely run pretty good when started cold without using a choke, but will also be a gas pig. Anybody that reads this will probably start going on about idle air bleeds- blah, blah, blah- whatever works for you.
Am looking to get a 78 buick with a 305 just has ifle off surge , what can it possibly be or does the carburator need adjusted since it had headers added on ??
I'll save myself some time by just posting this here instead of going through the comments one by one. This is a condensed version of the actual episode on the MT channel. There is a lot more information and they show a lot more of the processes they do to change the carburetors between runs to ensure the results are on an equal playing field. If you want to see that episode you have to pay to play.
If Vac vs double pump had the same air flow, and HP vs choke horn had the same air flow, how did you guys come up with two different reasons for the power differences. and why if with the Vac vs DP if your theory of fuel volume is correct, could you not just jet the Vac carb to match the fuel delivery?
Wish someone would cover the edlebrock/carters. I know they suck but that’s what fits on a duel quad 409 and I’ve never been able to get them to run right.
You guys need to spend more time explaining the fine details on the vac vs mech secondary test. On the surface it sounds alot like marketing for Holley selling more mech sec carbs. Hey, wait, how much $ does Holley pay you guys in advertising?
Oversized Holly carbs almost ALWAYS make more power ON A DYNO. In fact, often times they even out perform fuel injection. This has prompted every car guy on the planet to put a 1050 cfm dominator on their 283 small block. Unless you are on the track you are NOT driving wot at 7000 rpm and you’re killing power everywhere else. I’ll stick to my slightly under sized vacuum secondary carbs for superior driveability and power under the peak rpm. For me it’s all about excellent fuel signal ratio.
he did say that these types of carbs are sized to the application and RPM range bet if that vac secondary was an 850 then thered be a different story. mech secondaries USUALLY dont like being oversized like you say
@@tomcoon9038 The original 3310/780cfm/4150 carbs did have metering blocks with changeable jets, though, and had better downleg boosters. The later ones were rated 750cfm due to using straight leg boosters slightly restricting airflow and used a metering plate instead of the metering block making it a 4160 type carb. The 4160/750s are good carbs, too, if you know what to do with them. Quality control in recent years isn't so great, though, and parts such as linkages snap instead of bend when you attempt to adjust them.
Hey guys I watched this show on tv last nite and after being up all nite and busy with other things I finally noticed you used 2 different dyno mules not to mention intakes and who knows what all but I wonder if the numbers would have been at least a little closer and why didn’t you do a little tuning on the vac.unit since it came up short cause it was the lesser unit?like I said I was busy so I may have missed something you said but I was paying about 60%.
Such a good show my wife doesn’t agree but she sits there while I watch loved the 6bbl vs hemi. Have had both. Hemi looks better but my 440 on the street is better
I've wondered, too, but figured if yer gonna cut, might as well go all the way😁 Many years ago I used to do it with a hacksaw, then file, then clean up with sandpaper. Later in years used a dremel with cutoff discs in a flexshaft and then clean up. Now I prefer to use an electric choke and properly sized idle fuel restrictions for acceptable fuel economy.
I used to run a 454 with a Holley 850 with a Stub Stack on. I did The same with a 1050 dominador. Although i never knew if that would increase HP and torque.
The test with and without a choke horn is not completely accurate. Both carbs would show improvement with a K&N stub-stack, but the same principle would apply with a proper air cleaner base on either carb. The truth is, if you add a wall entirely around the airhorn that forces the airflow to drop straight down into the airhorn instead of entering from around the sides (as with a flat or non-existent air cleaner base), then the airflow is both better in volume and in flow quality. You can see this principle with your sink at home. With water flowing around the drain from all directions, you will get a "vortex hole" in the middle of the drain's flow. If you force the flow to enter from above , it will eliminate the vortex and allow straight-line flow. We do this with the bottom of the carburetor when we add a spacer. It does not just improve performance strictly because of the added plenum volume that may be needed, but by forcing the air through the carburetor in a straight line for a longer section. The longer the air is flowing straight before and after the carburetor's venturis, the better the flow and volume will be. That is one reason why "tunnel-ram" intake manifolds actually do so well. If the only air cleaner that can fit on your carburetor due to hood clearance issues is a small (less than a 3" tall filter), then the carb with the milled off choke horn is going to work better only because it will allow more airflow into the engine, even though it is a less efficient airflow than optimum. If you can, use a stub stack and a filter element top lid for the best performance. Been there, done that many times. The other issue - double pumper vs vac secondary : the double pumper is better designed for performance engines with camshafts for RPM/HP. Once you cross over a certain cam duration (depends on many variables, but usually around 220 degrees) the engine needs fuel added to the airflow instantly to complement the instant airflow allowed by the rapid opening throttle blades. The double pumper is designed to do that and if tuned correctly is basically a mechanical fuel injection system in operation. Vacuum secondaries cannot do this. They are "reactive" to airflow and always lagging behind the airflow curve by design. Great for torque because they constantly "size" themselves just a little smaller than optimum cfm at all engine speed and load ranges. Just not able to give the engine that maximum airflow upon demand instantly as the DP carb can do.
did your vacuum secondary carb have a metering plat on the secondary side of did it have a jet plate - Holley used to make a special metering plate specifically for the 759 vacuum carb and that makes a big difference in how it responds --- check that out
I think the same as you, but bigger jets alone may make the a/f ratio fat in some rpm ranges but jets AND air bleed size changes will alter the ratio curve at different engine speeds. It's the engineers' job at Holley Carburetor to accomplish. Are the lower priced carburetors intentionally designed to fall short of potential in order to encourage the user to upgrade to a more expensive model and make another sale? Sorry, Holley, but I believe that is the fact.
Seems to me you didn’t choose mechanical or vacuum secondaries based on horsepower but more to crutch up gearing for the street, traction issues, drivability and throttle response needs. If the carb is set up right, the accelerator pump is out of play once the pedal is down or you’ve got the wrong nozzle. A real 3310 (780 CFM) had different boosters and wasn’t crutched up to work on a small, choked down motor with no signal. They worked good on everything
The statement that you can't make the run good everywhere is wrong. It is done regularly, it just takes more time. Statement about better quality of air in regards to choke tower or not, is true. The vacuum secondary carb can also make the same power if calibrated correctly. Just make up for the fuel that is being pulled through the acceleration circuit on the DP.
I tend to oversized vac secondary for driving, just right sized (big AF) double to try to pull the most for performance. There is such thing as too big for a dp for a lower idle street/strip application. Just my understanding, tell me if I am wrong.
Street gearing and an automatic trans with a near stock converter: Vacuum secondaries. Everything else, double pumpers. I've been building carbs for 40 years.
We all believe you bro.
@@karenthomson9749 hes not wrong tho. double pumpers are great but vac secondary has its place too
I'm diamond 1
Vacuum secondary is fine for mild street applications, but the lag is a killer in racing.
Unless your spending the majority of your time above 5k, go vacuum secondary
What cracks me up is my buddies and me figured most of all this stuff , you guys talk about and test on all your shows. In the late 60s early 70s. All of use trying different things the hard way , racing each other, one step at a time. the drag strip times was our dynamometer. Really miss those times,we still talk about them, those of us still alive😢
It was all trial and error back then.
Strip tells the real story.
Back when parts were cheaper inflation wasn't so high, you could pick up parts just to test them on your own.. A Holley now is most of your house payment lol
What cracks me up is that people are *still* talking about peak power while completely ignoring drive-ability. Peak power is fine on a dedicated drag car but it doesn't matter very much at all on the street.
@rockets4kids frieburger said "Vacuum secondaries for street applications
You guys have the best show hands down. Great information, knowledgeable hosts and very entertaining! Keep up the great work.
The dyno numbers are impressive, but it really comes down to seat of the pants results. In my 69 big block Chevelle, vacuum secondaries with a 4-speed and 3.73 gears always gave me steady consistent launches. Switching to a double pumper carb, I only got good throttle response when I switched to a 4.56 rear gear. On the street, the launch was everything! Stop light to stop light never allows you to reach the upper power band. Street tires and the street itself were always the limiting factors as well as local law enforcement.
I really, really love this series. Excellent, useful, rigorous info, presented directly and to-the-point. Well done.
Great information. I had those same questions and, I agree with your answers!
The only other difference that you qualified in the beginning is, that (I.e.)a 750 carburetor would be the Minimum that carburetor would flow. It could actually flow much more in a given throttle body.
Great job gentleman!!
Great job as always, just converted to a choke-less carburetor recently, glad to see, there should be a little bit of a gain!
I’ve always been a fan of the tri-power setup.
Three Holley twos on a 428cj falcon was my money maker. With a 300 degree hydraulic cam it was capable of 7500 rpm. That was in 1972. The hottest setup for the street was the 406 3x2 induction for the FE engine.
I enjoy the stellar information and the banter. You guys are great.
What about comparison of the A/F curves between carbs? I was expecting to see that presented as the punchline.
well yeah its gonna be different in that no choke brawler that the vac secondary version.
@@KingJT80 Yes, I was expecting them to say that the HP difference was related to A/F ratio differences but that did not happen. They showed there was no difference in actual airflow, so I was left wondering what was the real reason for the significant HP difference.
@@rogermason5833 well they did mess around with the jets too off camera. Vac secondary couldn't make more power
The flow meter there using is not very accurate and even consistent, if it was it would be used as a flow bench
It would seem to stand to reason that if the airflow is the same and the fuel flow is different between carbs, the air/fuel ratio is going to be different. Which begs the question of how much and how much difference the different ratio makes. It's a really odd thing to completely ignore in the video.
I love this show, there needs to be more of it!
Very informative. I'll always use carb. Had a van burn up because an o ring on injector leaked. You never know when they go.
Glad to see my predisposition validated!!!😁
Thanks You Guys. There is hope getting my 750 Vac secondary no Choke Horn w. Metering Plate/Jets to work better.
The double pumper had the advantage of the air hat. You got the results you wanted by giving the DP straighter air flow.
My thoughts exactly. Air probably had higher velocity before entering the dp carb than it did with the vacuum secondary carb without the air hat. Like the old school velocity stacks, or Weber 8 stack system.
I built street/strip 440 my 66 Belvedere. Had 700 double pumper. I tweaked rebuild thermoquad 850. Boy did that thing run!! Never a hickup or stumble or anything. Ran flawless. Snappy throttle response and would keep pulling hard!! Im a thermoquad believer fanboy totally!
its not enough deference in power to make it worthwhile, I ran a vacuum 780 cfm on a super comp dragster 355 ci with horn still in place worked great interesting listening to it coming up on the brake. what shows up on the dyno is not always track information. thank you love the videos.
that 491 vs 514 is basically you saying you have a 500 HP small block as opposed to to saying yeah it makes almost 500 thats kinda a big difference. if i ran a mechanical secondary on the street (which i might still do) id run a choke. that i do agree theres no real difference vs running a true chokeless race carb even if it's the summer. 780cfm on 355 inches can and should run over 7000 RPM
23 PEAK HP difference on this test is almost a 5% increase, & the double pumper made more torque & HP from just below the test starting RPM all the way to max RPM. That's a pretty substantial difference. Double pumpers have zero disadvantage, "when properly tuned". I've always run them, since 1971 & never had a problem, even in cold weather, without having or using a choke. My current 750 Street HP on an Edelbrock Air-Gap intake & NO heat riser fires up & immediately idles in summer, takes a couple starts & hold the throttle slightly open in the winter, until the engine builds a little heat. My 500HP, 409ci SBC also gets better fuel economy than my computer controlled FI 2004 Tahoe. But, I will add that I've been tuning carbs for over 50 years & learned some big lessons in the early 80s working on highly tuneable Weber carbs, which the Holley HP series tuning is comparable to with their "air correction" jets!
@@bradgriffith4231 This test was done on an engine dyno. A chassis dyno with full accessories and you will never notice that 23 HP.
@@SOLDOZER If you think 5%, or 23 HP isn't noticeable in the vehicle & going down the track, you're very naive or have never raced. Pro Stock guys will spend $10,000 to find 1 or 2 HP with a motor that's already making 1,500 HP! 5% is a BIG pickup! BTW, our ALL MOTOR door slammer has gone 7.97/168 on race gas with 4,000 foot altitude air density, that's 7.70s/172 with 70* sea level air! How's your slug run?
@@bradgriffith4231 Nobody is talking about pro stock race cars here. We are talking about weekend cruisers.
I use a Quickfuel brawler 850 DP.on my Mopar 500 inch low deck with ported heads...it's also equipped with a ed's Victor single plane intake. I think this setup is bait for a dual feed carb! A vac sec carb can work it's just doesn't have the fuel curve of the DP...also Thompson perf atomizer plates on both ends of the dual feed carb really help in low end torque
I have a mild 318 in my Chrysler. Stock heads. 1980 model. It has a mild comp cam 268 h and edelbrock performer intake with an eddy 500 avs carby. Hei ignition with extractors and a full 2.5inch exhaust. Stall converter is a 2300 and diff ratio is 3:45 lsd truetrack.
I removed the choke butterfly from the front of the carby as this was a restriction and it certainly did make a difference on how it performs. Runs real well. Starts fine with no choke,just got to feather the throttle for maybe 30 seconds then it will idle happily. On the dyno as I had carby professionally tuned,it made 220hp at the tyres. Not massive but very good for what it is. I often wonder how it would change if I was to go for a bigger carby? Like a 650 perhaps? But they cost a lot so I won’t worry about it.
Great video by the way
🤘
would you not test the vacuum secondary with the secondaries jetted up? the hypothesis being that it should then match the fuel delivery of the mechanical secondary. maybe this way you get the better of both worlds?
Right...Like was mentioned the air velocity draws fuel from the accelerator pump discharge nozzles / circuit once the throttle blades are fully opened. They continue to flow fuel. I have seen that occurring on camera footage before of carburetors running on a dyno. One of these days i'm going to mount my go pro under my hood to see what goes on. I've spent a lot of time tuning my junk using both vacuum secondary and double pumper carburetors.
Story.
One tuning session after I put my AFR gauge in the car I was working with different power valves. Changing different ones in and out for hours. Driving and observing. Nothing was effecting the readings. I took off the front bowl and metering block again...I was starring at the metering block. Looking at it in disbelief. Just starring for like five minutes. When I saw what the problem was.
Holley did not drill the power valve channel restriction holes in the metering block !
DUH !
@@superfuntime3107 ohh, boy😡
There was one I'd like to see in addition to this - that is how much bigger do you have to go in vac secondary carb size to negate the double pumper advantage?
Why? The HP loss is negligible from a street to strip application. Use what the application calls for.
@@joshtheking1772 Oh I see, because you don't see the need for a test like this then it doesn't need to be done.
@@ThePaulv12 maybe instead of relying on free entertainment to do it for you, you should do the test yourself and then enlighten everyone else for free
the mech secondary shows more fuel and power over vac sec. can you increase sec jets in vac and make about the same hp as mech?
Ok so what if you have a vacuum secondary carb with a metering block were you can change jets and give it more fuel on the secondary side?
These are thing I struggled with early on. Eventually I ran Choke carb tuned for winter. Then a different choke horn delete (sawed off and polished away) carb tuned for summer. This was before you could get a "race" carb with that done already. The double pumper horn delete was for summer. Vac sec for winter. They ran the same in the environments they were tuned for. Nobody knew.
or,
now you can get a chokeless carb with vacuum secondaries!!
I had a 62 nova straight 6 that in winter or summer pump twice and she'd start and idle no chock. With engine hot just turn the key. That car would idle all day and not skip a beat, smoothest carbureted vehicle I've ever had.
Could the fuel difference not be that the spring in the vacuum secondary carburetor is too stiff and if you installed a lighter spring the secondary would open quicker and be closer in power to the mechanical secondary?
You guys could've just made a phone call to AED Performance in Richmond VA and they could've saved you alot of time and explained the difference to you and how and why one would make more power over the other per application. Those guys are very knowledgeable and have been doing this stuff for many years
The double pumper is always the way to go if you're willing to put the time into tuning it
Agreed .
Double pumper waste of time for street application.
@@SOLDOZER depends on the combination
It is possible to get an anti siphon squriter nozzle. These were used on factory emissions era carbs.
Great show, I always enjoy it. Just started rebuilding my 850 double pumper from my 455 Firebird a couple of days ago ...
If the double pumper is adding more fuel (via siphoning through the a/p discharge nozzles) to the same air volume, the mixture is richer. Why not enlarge either the main jets or the power valve restriction in the vacuum secondary carb to achieve the same fuel/air ratio?
While that would have been worth testing, it seems their criteria at the onset was to test apples to apples from the factory instead of fiddling with them whatsoever. I bet you could compensate a bit for what the vacuum one lacks in and probably pretty easily so it’s disappointing they didn’t test for that.
The problem is distribution in the Vacuum Carb vs the DP. It's more than just the volume of fuel added by the siphoning. It's also distribution. You've got 4 separate barrels in both carbs. All the same size and physically in the same spot geographically speaking on the manifold to which they are bolted. This is where the similarity ends though. While air flow is the same in both the ability to atomize and mix fuel is different. ALL THE FUEL supplied in the two primary barrels of the Vac Carb must mix with air supplied by all 4 individual barrels of the carb. The front two will supply a little bit richer mix to the cylinders supplied most by the air coming from the front of the carb and the cylinders mostly supplied by the rear bowls will be just a tad leaner. It's a trade off you accept for the drivability on the street. The mechanical carb supplies fuel to each of all 4 barrels and this no doubt gets you a much more even distribution of air and fuel both to every cylinder.....while not perfectly even you can bet it's far closer to even than the Vacuum carb will ever be capable of. As Steve B points out: you could richen up the primary circuit of the Vac carb but you'd lose all you drivability in the attempt and it still wouldn't work as well because while you may actually resolve "lean" in some cylinders it'll almost for sure enrich, past ideal, in those that were properly supplied before you richened up the primaries. Bottom line: This is why computer controlled injectors above each cylinder are how it's done on modern engines. With a Carb you can't have both. You gotta pick. Street or Strip one carb is going to be vastly superior to the other depending on your priorities. The vac carb can't match the WOT performance of the Mechanical and of the flip side the Mechanical will never be able to match the street manners of the Vacuum Carb. You gotta know which is more important to you ahead of time.
Best series ever! I miss it from it was here on yt...
For me, in Colorado, we need choke just nature of the beast. Anyway I firmly believe dbl dumper on the track, spread bore on the street. A vacuum secondary just works better in stop and go driving.
If that's what you think, you're tuning them wrong
QUESTION ... between the vacuum and mechanical carbs you measured the air volume to be exactly the same and measured the fuel flow to be dramatically different ... especially on the secondary side. You put the difference in fuel delivery down to siphoning fuel thru the discharge nozzle .... which is fine.
But given that the volume of fuel ingested looks to be around 20+% LESS at some points, surely this would show up a lean condition in air/fuel ratio ???
So why can't this be tuned out of the vacuum carb ???
If the vacuum secondary carb flowed less fuel in the secondary, was the AFR leaner? Would increasing the jets help the power?
@@bigboreracing356 Brawler series does.
@@bigboreracing356 - There are jets in the secondaries. However, there is no accelerator pump.
No. Both carbs would be providing the same air/fuel ratio and adding more fuel to either would just cause an over rich mixture ratio and possibly lose power. The DP carb is pro-active in that it squirts the required amount of fuel into the incoming air ahead of the curve which is why it allows better performance to begin with. The air and fuel enter instantly and are predetermined by tuning. No restriction equals maximum air/fuel inducted into the engine. The vacuum secondary design is a reactive design that restricts the airflow to an always less than maximum so that it can use the throttled engine pressure differential to initiate and maintain fuel flow to match the airflow. This can give good torque and is easier to tune to prevent "bogging" but it comes at the cost of limiting the engine to always less than maximum induction for any given load and RPM condition.
@@reason2gether you did not watch the video carefully nor do you understand how this works.
@@bigboreracing356 LOL - still wondering what the AFR differences were.
I enjoyed this half of a third of an episode.
would of been nice to see air fuel ratios of the double pumper to the vac. secondary carb. Great info to see though! Love my double pumper on my Cuda!
This. The primaries are working a lot harder/likely not metering as well as the secondary in the vac carb. I am guessing proper jetting would even these carbs up but ultimately the DP would be making more horses. Have a look at the secondary butterflies on a dyno engine you will see how they open/close depending upon vacuum and the diaphragm/spring setup.
Need to compare manifold vacuum for each run. My guess is that the more restrictive carburetor versions will flow the same amount of air, but at slightly higher vacuum. That higher vacuum would sap some of the potential horsepower.
When I was a kid ,dad pulled the choke blades out of some carbie he had on a 350 Chev.ever since then iv pulled out choke blades on single barrel strombergs,twin barrel webers and on and on until I figured out how to zip tie Rochester primary to the secondaries links all barrels at once lol .Now im tuning Nissan RB motors with a lap top here in New Zealand
I had a brand new 3310 vacuum secondary on my mild 383 right up until some chassis dyno time. The shop had a used 650 dbl pumper on the wall and after throwing it on the car I promptly bought it. WAY more stable AFR from the 3310 and I had all the springs and quick change kit. And this was a 3.08 geared, auto, mid 14 sec car.
Dyno "tuning" is a waste of time & $$$$ because there is nothing about the climate conditions or loading on a dyno that actually simulates real world street or track driving. NASCAR engine builders look more a the time it takes to accelerate the engine from bottom "track" RPM to peak RPM rather than peak HP with the load being the simulated vehicle weight & overall gear ratio.
@@bradgriffith4231 guess you ignored the part about AFR jumping all over the place. AFR is AFR. Everything you said may be true but gauge readings are true as well when used comparatively. Clearly one carb was consistent with fuel delivery and one wasn't. Nothing but truth in that observation.
@@madrew2003 Maybe y'all ought to learn how to properly tune a carb if your AFRs were constantly changing. Regardless, dyno tuning is a waste of time & $$$$ because there's nothing a dyno does that remotely resembles real world applications, whether on the street or track. Pro Systems will build & correctly calibrate a carb to perfection & ya won't even have to touch the A/F mixture screws or curb idle speed without even seeing the car, IF ya tell them the truth about your engine specs, vehicle, & altitude where it's normally raced.
@@bradgriffith4231 you sure do like to beat that drum, don't ya? Give it a rest. I use a wideband gauge to tune my carb and the trap speed at the track. Does that make you any less cranky?
Great information! I have to of the same carbs one vacuum and one mechanical. I’m gonna put the mechanical on and try it out
I appreciate all the information. It's fascinating. But I could read results faster. I watch because I love hearing engines pushed against a dyno.
I´d like ro know if the AFR was the same. If it´s "leaking" through the acc pump but the airflow is the same the dp should be a bit richer, meaning the jetting the vacuum carb should put out the same power. Yes?
Exactly ... just asked that question, then thought I'd read some comments and see if anyone else picked up on that .... several have.
AND it only makes sense to me that purposely enriched mixture through a metering circuit designed for the job and dispersed through the booster to atomize correctly would be better and more consistent than fuel "accidentally" admitted into the airstream through the accelerator pump squirter😵💫
Engine masters breaking more myths! Awesome show, awesome series!
Great episode guys. Informative as always. Thanks.
First, your shows are so therapeutic! Thanks! Anyway, was wondering how much of a difference a drop-base air cleaner would have made in these tests...especially with the choke horn?!
Yes, which is more critical? To have a less than optimum intake manifold that fits comfortably under the hood topped with a free flowing air cleaner, or to have a tall, high flowing manifold that requires a low profile air cleaner and especially when used with a choke tower equipped carb? Years ago it wasn't a hard decision to install a scoop or change the hood on our cars, but today a factory appearing classic is very desireable.
That was a really useful & interesting comparison. Well done😊
THANK YOU SO MUCH. I LOVE TO LEARN ABOUT CARBURETORS!!! SO MUCH FUN!!! GREAT VIDEO AND THANKS FOR SHARING!!!! I LEARNED SO MUCH!!!!!
Perfect group of tests for an old KnN Stub Stack. (I dunno if they were any good)
Wonder if jetting the primaries and/or going up on the secondary metering block would bring it closer the double pumper
The VS Brawler needs a “White” secondary actuation spring in the pod. Also the brawler should be tuned via jetting and air bleeds to compete more accurately/similarly.
So this test needs to be clarified “Out of the Box” comparison only.
hey you 2 , how about a dyno run utilizing a correctly cfm rated carb with the exactly correctly rated primary and seconday jets on a 2 barrel then 4 barrel carb
I'd like to see you guys run tests on different types of air cleaners. Like an open top element, an old paper enclosed stock style, a velocity stack style element and a forced induction carb hat.
They did that a few years back.
And the paper fram was just as good as the rest lol
@@dakotaautosales9673 But not as good as the salad bowl
@@dchil15 ???
@@dakotaautosales9673 Did you even watch it? They took a salad bowl, cut the bottom out and made hp with it.
I have a Chevy 350 two bolt main. Headers and bored over 30.. what would be the best carburetor for this combination? Street car.. but I want a lot of torque and horsepower.
670 holley street avenger
I daily drove a 650 double pumper for a year and a half with the choke horns milled off and it never once gave me a problem as long as I drove it at least every other day even in the winter. I highly prefer how they drive with a manual over a vacuum secondary, but that’s my preference.
Same here I ran a 600 dp on a mild 360 automatic , it ran flawless .
I went with the mechanical because my motor has less then 10inch of vacuum with the radical cam.
Patrick with PRO Systems can make them work across the band for sure! I've never had an engine run better with any other Carb
have u ever ported the cam bearings to get a bigger cam in a sbc or season a block or polished the inside of the block for faster oil drop or put over sized cylinders in a sbc or use aluminum titanium alloy rods or balance all the parts rods pistons so on then balance the piston and rods to the counter weights then balance the crank with fly wheel and balancer. u guys should try this it will do insane rpms if u try this port all the ports oil water so on then port the heads open up the intake ports and match the new intake ports to the heads but u will need to go bigger on the cam so u will have to go over sized bearing on the cam when we did it back in eary 90's the custom roller cam just the cam was over 1000 bucks and u will need titanium locks on the valves. we did this to a 327 i helped but bell blue printed and built the engine he also went with tunnel ram with 13.5 to 1 compression for pump gas only 92
The difference from the vacuum secondary also is no back metering block and the four corner idle. Metering block possibly adding more fuel for the secondary system??
Dual circuit Dominator 1050 cfm'er. = +4 mpg over dialed in 4150. Had 11 mpg with 4150. Now has 15mpg with dominator. Chevy Nova.
I run a Holley 670 avenger on my 428 C.I. Mild cam street Engine. It works perfect for me. A Holley Avenger Carburetor is a type of performance carburetor that is designed for street and off-road use. It is not a double pumper, which is a term used for Holley carburetors that have two accelerator pumps. A double pumper carburetor is more suited for racing applications, while an avenger carburetor is more user-friendly and adaptable to different driving conditions. Most people are non racers.
Aside from maybe being a bit on the small size for your engine, it CAN be tuned for serious performance and still get decent fuel economy. From my experience with the Street Avenger, the idle system is calibrated on the lean side which is fine(and desireable) for a mild engine and highly advised to use a choke for cold start & idle. When you start adding a cam and a bigger manifold- especially an unheated one, the idle system calibration will likely be too lean and not only will it be difficult to achieve a good idle but will also be difficult to eliminate an off idle stumble and stomp on the pedal pop through the carb. The fix would be to open up the idle feed restrictions in the metering block a few thousandths of an inch such as going from .028" to .031". If your idle mixture screws need to be turned out as much as 2 turns, performance would probably benefit by increasing the idle feed restrictions by a couple thousandths. I like to shoot for 1-1/2 turns out. Often when a performance carb is put on a mild engine, the mixture screws require less than a turn out for best results. That carburetor will most likely run pretty good when started cold without using a choke, but will also be a gas pig. Anybody that reads this will probably start going on about idle air bleeds- blah, blah, blah- whatever works for you.
Am looking to get a 78 buick with a 305 just has ifle off surge , what can it possibly be or does the carburator need adjusted since it had headers added on ??
I'll save myself some time by just posting this here instead of going through the comments one by one. This is a condensed version of the actual episode on the MT channel. There is a lot more information and they show a lot more of the processes they do to change the carburetors between runs to ensure the results are on an equal playing field. If you want to see that episode you have to pay to play.
Air filters are offered in different heights from K&N. I wonder how much taller the filter has to be to eliminate the drop in hosrepower?
I wish they would do a Holley vs predator ..I ran every carb possible..not newer than 1997 the predator was wild responsive
does the vac barb need bigger jets in secondarys ,,?
Can't change Secondary Jets if it has a Metering Plate, Metering Block, Yes, Plate, No.
@@badass6.0powerstroke10 You can open the restrictions .002" or .003" at a time, though.
Having trouble setting gas ratio to my 650 double pumper on my rebuilt sbc350 any videos or tips
You guys should test out a Weber carburetor setup on a big block. Tune each cylinder and optimize it
If Vac vs double pump had the same air flow, and HP vs choke horn had the same air flow, how did you guys come up with two different reasons for the power differences. and why if with the Vac vs DP if your theory of fuel volume is correct, could you not just jet the Vac carb to match the fuel delivery?
Because they want to help Holley sell their more expensive products for their own gain.
Love my Holley Street HP 750. Best carb I’ve ever owned, bar none!
I will say also I have a Bugcatcher scoop sticking out the hood so clean cool air is going into the motor going down the road.
Wish someone would cover the edlebrock/carters. I know they suck but that’s what fits on a duel quad 409 and I’ve never been able to get them to run right.
You guys need to spend more time explaining the fine details on the vac vs mech secondary test. On the surface it sounds alot like marketing for Holley selling more mech sec carbs. Hey, wait, how much $ does Holley pay you guys in advertising?
I hit the thumbs up button several times but it only scores once👍
@@mickangio16 I got your back
Would've been nice to know the cfm rating and the engines CID
Oversized Holly carbs almost ALWAYS make more power ON A DYNO. In fact, often times they even out perform fuel injection. This has prompted every car guy on the planet to put a 1050 cfm dominator on their 283 small block. Unless you are on the track you are NOT driving wot at 7000 rpm and you’re killing power everywhere else. I’ll stick to my slightly under sized vacuum secondary carbs for superior driveability and power under the peak rpm. For me it’s all about excellent fuel signal ratio.
he did say that these types of carbs are sized to the application and RPM range
bet if that vac secondary was an 850 then thered be a different story. mech secondaries USUALLY dont like being oversized like you say
Why not add a secondary pump nozzle to the vac secondary carb, that can be blocked off or used if desired?
What would happen with the vac sec if you changed the back boosters to a larger size to compensate for the discharge nozzles extra flow
I love this can we expand this? LIKE GIANT 4BARREL VS DUAL QUADS VS 6 PACK.??? DI MORE CARBS = MORE POWER?
You guys absolutely rock
How you gonna run the vac-sec carb without the air hat, and the DP with it?
Did the vacuum secondary carb have a metering block?
If it's a 3310 then no. They had plates.
@@tomcoon9038 The original 3310/780cfm/4150 carbs did have metering blocks with changeable jets, though, and had better downleg boosters. The later ones were rated 750cfm due to using straight leg boosters slightly restricting airflow and used a metering plate instead of the metering block making it a 4160 type carb. The 4160/750s are good carbs, too, if you know what to do with them. Quality control in recent years isn't so great, though, and parts such as linkages snap instead of bend when you attempt to adjust them.
Hey guys I watched this show on tv last nite and after being up all nite and busy with other things I finally noticed you used 2 different dyno mules not to mention intakes and who knows what all but I wonder if the numbers would have been at least a little closer and why didn’t you do a little tuning on the vac.unit since it came up short cause it was the lesser unit?like I said I was busy so I may have missed something you said but I was paying about 60%.
Because their job is to sell the higher priced piece😊
Such a good show my wife doesn’t agree but she sits there while I watch loved the 6bbl vs hemi. Have had both. Hemi looks better but my 440 on the street is better
Instant TORQUE😊
I wonder if cutting off outer side wall of the choke body
I've wondered, too, but figured if yer gonna cut, might as well go all the way😁 Many years ago I used to do it with a hacksaw, then file, then clean up with sandpaper. Later in years used a dremel with cutoff discs in a flexshaft and then clean up. Now I prefer to use an electric choke and properly sized idle fuel restrictions for acceptable fuel economy.
You guys are amazing 🙌🏻
I used to run a 454 with a Holley 850 with a Stub Stack on. I did The same with a 1050 dominador. Although i never knew if that would increase HP and torque.
They dont. Its a gimmick that faded away
i'm with these guys in the opening comments. I had an AFB on my slant six
Good episode, thanks for sharing. 🙂
Why don't just change the spring in the vac scend dairy to make it open faster and see what the difference is and put a scend dairy meter block on it
The test with and without a choke horn is not completely accurate. Both carbs would show improvement with a K&N stub-stack, but the same principle would apply with a proper air cleaner base on either carb. The truth is, if you add a wall entirely around the airhorn that forces the airflow to drop straight down into the airhorn instead of entering from around the sides (as with a flat or non-existent air cleaner base), then the airflow is both better in volume and in flow quality. You can see this principle with your sink at home. With water flowing around the drain from all directions, you will get a "vortex hole" in the middle of the drain's flow. If you force the flow to enter from above , it will eliminate the vortex and allow straight-line flow. We do this with the bottom of the carburetor when we add a spacer. It does not just improve performance strictly because of the added plenum volume that may be needed, but by forcing the air through the carburetor in a straight line for a longer section. The longer the air is flowing straight before and after the carburetor's venturis, the better the flow and volume will be. That is one reason why "tunnel-ram" intake manifolds actually do so well. If the only air cleaner that can fit on your carburetor due to hood clearance issues is a small (less than a 3" tall filter), then the carb with the milled off choke horn is going to work better only because it will allow more airflow into the engine, even though it is a less efficient airflow than optimum. If you can, use a stub stack and a filter element top lid for the best performance. Been there, done that many times.
The other issue - double pumper vs vac secondary : the double pumper is better designed for performance engines with camshafts for RPM/HP. Once you cross over a certain cam duration (depends on many variables, but usually around 220 degrees) the engine needs fuel added to the airflow instantly to complement the instant airflow allowed by the rapid opening throttle blades. The double pumper is designed to do that and if tuned correctly is basically a mechanical fuel injection system in operation. Vacuum secondaries cannot do this. They are "reactive" to airflow and always lagging behind the airflow curve by design. Great for torque because they constantly "size" themselves just a little smaller than optimum cfm at all engine speed and load ranges. Just not able to give the engine that maximum airflow upon demand instantly as the DP carb can do.
did your vacuum secondary carb have a metering plat on the secondary side of did it have a jet plate - Holley used to make a special metering plate specifically for the 759 vacuum carb and that makes a big difference in how it responds --- check that out
Thank you and well done !
Well, I'll I've got to say is, Demonstrates what happens to the power if you only know how to bolt shiny things on out the box.
Best comment😊
I wonder though. If thr only difference is fuel wouldn´t bigger jets on the secondary take care of the difference?
I think the same as you, but bigger jets alone may make the a/f ratio fat in some rpm ranges but jets AND air bleed size changes will alter the ratio curve at different engine speeds. It's the engineers' job at Holley Carburetor to accomplish. Are the lower priced carburetors intentionally designed to fall short of potential in order to encourage the user to upgrade to a more expensive model and make another sale? Sorry, Holley, but I believe that is the fact.
Seems to me you didn’t choose mechanical or vacuum secondaries based on horsepower but more to crutch up gearing for the street, traction issues, drivability and throttle response needs. If the carb is set up right, the accelerator pump is out of play once the pedal is down or you’ve got the wrong nozzle.
A real 3310 (780 CFM) had different boosters and wasn’t crutched up to work on a small, choked down motor with no signal. They worked good on everything
DOES HOLLEY STILL MAKE THE 1050 DOMINATOR CARBURETOR? THAT WAS USED ALOT ON THE PRO STREET CARS FROM THE '80s.
The statement that you can't make the run good everywhere is wrong. It is done regularly, it just takes more time. Statement about better quality of air in regards to choke tower or not, is true. The vacuum secondary carb can also make the same power if calibrated correctly. Just make up for the fuel that is being pulled through the acceleration circuit on the DP.
You should set up a Schlieren optics in front of the carb to see the flow of air difference.
when are you planning on testing the new edlbrock holley style carbs
I tend to oversized vac secondary for driving, just right sized (big AF) double to try to pull the most for performance. There is such thing as too big for a dp for a lower idle street/strip application. Just my understanding, tell me if I am wrong.
Can you guys do a test on the Holley 750 Double Pumper vs 750 HP Double Pumper vs 750 Holley Dominator?