The Myths And Realities Of Carburetor Sizing- History Proves The Formulas Don't Work
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- Опубликовано: 6 окт 2022
- Calculating cubic inches and volumetric efficiency to arrive at the correct carburetor size for any given engine combination seems like a reasonable way to go about things, and is ok when dealing with a completely stock engine, but when you start trying to make real power, it will leave you wanting a bunch more.
Here's a rundown of some of the factors at play, how the manufacturers chose carb packages, and a few basic guidelines that will get you going in the right direction.
#Holley #edelbrock #classiccar
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Did anybody else look at the Holley carburetor on the left side of the screen and wonder why the bolt for the air cleaner was so long? Then I realized there's a jack back there that's just lined up perfect LOL
Same lmao
Yeah, me, too.
Yeah my old 47 yo eye are .....weall just say I need to eat ton of carrots 🥕 😅
As a young hot rodder I love this kind of video! I would love to hear your just tell stories about the old days of hot rodding and what it was like. The history is so interesting to me!
If you haven't you should watch his video on street racing in NY during the 70s
I use to run with the Street Racers while "Big Willie " was president . This man was directly responsible, with some others for bringing drag straps into California.
As for me, I saw the closing night of the original Lions drag strip. I was there for the opening night of the new Lions, and I raced the last night of that venue.
There's a story for you.
@@raiderjohnthemadbomber8666 very cool sir! Hopefully we get another venue here in California soon instead of the irwindale 1/8 mile
@@KJ_Moore
Yeah, I hope so too, even though I don't live there anymore. So anyway, I've also visited and raced at Irwindale and OCIR, which had powered rollers in the staging area for anything without a starter. But Lions was my home turf, as it were. Good luck with whatever you're building. Currently I'm running a 74 Nova with the original small block. I've managed to get 536 hp out of it. It runs high 5s in an eighth. This'll probably be my last hot rod build. I'm hoping to get two more things built before my body refuses to help me. It and I are currently having creative differences. Hey, what are ya gonna do?
@@barneymiller7894 11
Years ago I had a auto shop and also specialized in high performance tuning for street cars and drag racing. A good example: one customer had an 86 Monte Carlo SS that he drag raced. He didn't have the budget for an engine so we kept the 305, ported the heads, swapped the cam, installed an old Torquer single plane intake and a Holley 850. Everyone told me I was nuts it would not work. We proved them wrong! The engine was run up to 7300 RPM at the track and worked great. (Until the stock bottom end let go) Then I gave him a built 327 I had laying around.
I’ve got a 305 in my Grand Prix (Monte Carlo with some more chrome) and people underestimate them. They’re not power houses, but with a few mods they can be made into formidable motors. I want to do cam and heads soon, but I’ve got a lot of projects right now.
NEVER worry about your videos being too long. I appreciate your time and sharing your wealth of knowledge. There is a saturation point on learning. I bet some of the people who dropped off come back and watch this video again..and again!
In the late 80s my buddy had a 79 Mercury Capri. We built a 2.3 Ford 4 cylinder rubber band motor.Punched .040, 10.5 :1 TRW forged pistons, ported the Hell out of the head, nasty Melling cam, home-made single plane intake with a 430 cfm Holley 4bbl, Ford Motorsports catalog header and flywheel, with a 4 speed. We went through allot of clutches. We stood it on the back tires regularly on slicks.
You saw daylight underneath the front tires with what sounds like a 210 crank hp manual 4 speed Fox? Really? Did it ever break out of the 13s?
Yup we have built a few for dirt cars, they are surprisingly decent
Thats awesome! I'm thinking about building a 2.3 for my '65 Falcon! It's currently got a 200 six in it but I estimate the 2.3 would give me even more room under the hood and save on weight! And there seems to be more aftermarket support for the 2.3!
@@jaylestingi5418 Troll.
The 200 is just a sad motor unless you're ready to pick up parts from Australia. They build some screamers out of 200's down there. The 2.3 still has such a following that the go fast parts are out there. Be a screamer in a Falcon.
12:38 - “What did I do, I broke it!?” This reaction, and result, is a big reason I like your work. Genuine AND reasonable reactions to twists and turns. Exciting things happen and it’s no worse than you grabbed a cold coffee versus a hot coffee… Just drink it and plan better next time. Perfectly and perfect.
My brother had one of those 2.0 Pinto engines in his Mk. III Ford Cortina - with just a cam and a DCOE Weber it would rev to 8k. Made for an amazingly quick car despite the perceived lack of cubes. 👍
I talked to Norm many times about the beginnings of his racing. The first car to actually have his name on it was a customer’s car, it was a super stock dodge that ran indoors at the amphitheater. He put the name on the car in return for spark plugs and tune up parts for that same reason. The “mr norm” name wasn’t painted on there, it was on a cardboard sheet. Soon after norm had his own team who later on ended up becoming the chi town hustlers. Oh, there’s a pic of that car online showing it running inside at the amphitheater.
I had some very interesting conversations with Norm back in the 90's. Did a five page feature on him for Super Stock magazine back around that time.
@@UncleTonysGarage I have that article. Many awesome conversations were had as we drove hours to car shows, I learned a lot from him that I will never forget. The best stories were from the days of match racing the 65 AFX car that he acquired from Roger Lindamood. He purchased the butch leal AFX car and was going to run two AFX cars, sadly it was crashed in epic fashion. Funny what can happen when creativity gets involved with young car guys in the late 50s/early 60s out of their dads gas station…
Fords cross Boss for the 302C, the 406 Tri-power, they had 3 350s, put a pair of 500s on the front and rear they make 425 hp they claim the 427 made, if you replaced the 2x4, on the 427 LR, put a pair of 750s on it. 500 hp instantly . OT/Pull on the choke lock Carters do that
I took an 87 Olds Cutlass Supreme with a 3.8 Buick V6 and a TH 220 tranny, up graded to an Edelbrock Performer setup with a 600 cfm, TH200R4 2200 rpm stall lockup converter and made it streetable (broke motor mounts every 3 months) and got it to give 30 mph. there were other mods but you are so right in that we threw away the formulas and went with our gut feelings for what was wanted. Please keep teaching this younger generation about what is really going on and less techno-junk, formula junk. Ah, for the fun of the 60's and 70's!
One of the reasons I like Quadrajets is the ability to tune the secondary air valves and metering rods for maximum performance and use the primary side for driveability and economy. It does need a cut down, dropped float for sustained high rpm or it will starve.
I love Q-Jets. I developed a conversion to make early models dual feed. It works only at wide open throttle using a solenoid from a Nitrous kit and a throttle activated switch. I have a cust with a 540 BBC in a 70 Pro Street Camaro that has gone 8.80's with it.
I started with a 500 Caddy main body & airhorn which flow 1bout 900 CFM.
I lobbied NHRA & IHRA to make it legal but the politics play into it and they won't allow it.......some slick guy could possibly hide it if he was clever, but the float bowl capacity is the drawback........
I actually have a better way to control the air valve.......starting doing this in the 70's.
Use a long air cleaner stud and locate a spring appox .500 inside diameter that will fit over the air cleaner boss and sit on the hanger. I use ones that have about the same tension as a pump return spring........anywhere from an inch or so as long as it fits the air cleaner.
Put a 1/4 washer on the spring and I use a snug fitting wingnut. Loosen the stock air valve tension so the valve is really floopy but does return on it's own. Put some tension on the new spring and try it. You can now adjust it without playing with the stock hit or miss stock system.
Some Q-Jets I have to modify the air cleaner boss so the spring doesn't bind, but I do this on any car where tuneability is key. You'd be shocked at how well it works. I use a drop of Locktite red so the stud doesn't move.........
I'm using a Quadrajet as a blow through carb on a turbo'd 5.7 Vortec and it works great.
@@quietcool4884 we need to see a video of that! There were no cheap handy cams back in 1985 when I did mine.
Had me ah robchester quadrajunk once. Made a killer trot line weight🤯
I grew up watching quadra Jet carburetors cycle across my father’s work bench.
He worked for the railroad following several years as a mechanic with both GM and Chrysler.
He loved those carburetors. I don’t know how many people that would praise him for getting their fuel mileage back.
Several of his old drag racing friends that were still in the game would pass through town every year or so. That was always fun.
I remember several instances of them trying things with these carburetors through the years. As a kid I would just begin to think I had a basic grasp of what was going on with them, then I would see these experiments.
Some worked others not.
I’ve tried my hand at building a few. I could get mileage out of them at best mostly sealing the metering wells.
I’d ask my father what to do when I had rebuilt one. His answer was always the same. “Keep screwing with it until you understand there is no magic wand for these items.”
I just never had the patience to mess with them for very long or he would get tired of watching my frustrations and take over. By then I was spent. I never remember it taking him more than a few minutes to straighten out what I had done.
I’ve seen him and many knowledgeable carburetor tuners get into fights with various carbs of other types. Just don’t remember too many with these men and Quadra jets. Sure there were some worn throttle shafts that they were tooled up to repair back then but they could quickly identify that even I could.
One thing is for sure. It takes patience and tenacity to use a carburetor effectively.
I recently bought an old 4500 dominator 750 cfm.
Dad marveled over the 750. Sat down and took it apart and gave me a list of parts to order and told me to get it cleaned up and ready.
Damn if that wasn’t expensive……. Still yet it’s been fun to sit and visit with him over it.
I hope to have the patience now. I’m 52 dad is 77 and still getting up every day looking for something to get into.
Rough tough and gruff. There’s no doubt that instant gratification has taken its toll on my father’s posterity. Mine as well.
I feel like my life isn’t going to be quite complete until I learn how to be patient and correctly tune a carburetor.
I run the factory numbered Thermoquad on a stock 340 with headers. Max flow on the small block Thermoquad is around 800cfm, sounds like a lot but the carb only gives the motor what it needs. That's the beauty of vacuum secondaries.
Same carb I have on my big block, runs fantastic!
And it's not vacuum secondaries, it's an air door like a quadrajet. Punch it WOT, all the butterflies are open no matter where vacuum is. The air door does the compensation for secondary transition.
Here's my take on the formulae used by the aftermarket to determine the recommended CFM for their customers: The manufacturers grossly undersize the recommendation for the sole purpose of reducing warranty replacements. That's it in a nutshell. An undersized carb will perform well and the customer will be happy and won't wish to return the carburetor to the manufacturer with a scalding message attached to it or (in this day and age) post on the interweb how crappy the carb is.
Every time Tony starts talking about stuff like this I want to go out and start my 67 Impala SS just to play with the accelerator !
Your wisdom, knowledge and ability to explain the depth of the the physics behind making something run is astounding.I am super appreciative of everything you've shared and look forward to everything else you will share with us. I look very much forward to more of the carburetor talk
I would like to hear more about mechanical and vacuum secondaries and when to use them.
@@jonathanlawson4667
Also to add to our comment- I grew up being told by alot of racers, mechanical 2nds are better w standards. Vacuum 2nds better w automatic
Vacuum secondaries don't work well with a manual transmission because the throttle action is off/on/off/on much faster than the secondaries can actuate.
Why not stick with mechanical secondaries and drive with your foot, forget a vacuum secondary.
Also, an air door like you'll find on a quadrajet, isn't a vacuum secondary.
Vac 2nd... never use em!
Always use a mechanical carb ! If performance is your goal
Its often a matter of preference. On a dual plane manifold you can often get away with an 800+ carb with vacuum secondary or an air flap etc.. even on a moderate engine, these manifolds often show extra power when you increase the carb size. But with a single plane you might not find extra power using a large carb even if you are making more top end power than you could make with the dual plane, they often dont see gains from makking the holes bigger than they need to be. and as long as the transmission agrees the "right" carb might not need to be vacuum secondary. That's not to say you cant use a sensible mechanical carb on a dual plane or a vacuum secondary on a single plane to improve drivability a little. It sounds backwards that youd use a bigger carb on a less powerful engine and a smaller carb on a high revving engine but the manifold designs respond very different and have different pulse energy. And you may be more inclined to use the low speed power of the dual plane wanting the vacuum secondary there to help out if you floor it with a tight converter and a governor that doesn't encourage it to stay in a lower gear long enough or you just don't feel like downshifting and short shift as you cruise. But if you like the engine rev happy and your trans is tuned or you manually shft accordingly you may not feel you need vacuum secondary and may want the instant input of the mechanical carb.
First of all thank you for all of your knowledge. I am a Chevy guy but I watch all of your videos religiously! I agree with this video totally. I bought a new 950 holley xp for a 60 over 396. People were saying it was too much but it ran great. My argument was that the engine is only going to use what it needs and if I upgrade cubic inches later on I will be 👍
There is some truth to the engines only uses what it needs carbs depend on the signal from the engine and oversize too much you lose signal which effects driveability.
Tony, I always wondered about that! In the 70's I had a 340 Cuda drag only that ran high 11's. I had a tarantula manifold,12.2:1 compression, .501 lift cam with a holley 850 double pumper. I bought a holley carburetor book and doing the formulas it said I should have a 650 CFM carburetor on it. So I sold the 850 and put a 650 on it. Brougher's speed shop told me that was a big mistake. I should have listened to them, it was! Thanks for finally explaining that and holley should have never put that in their performance carburetor book!
Some day someone explain to me what a "tarantula" manifold is.
I always like when you do these type of videos, I don't care if it's a longer video.. I don't really think about the time.. I like longer videos personally.. It's not really the length but as long as the content is valuble.. The time steps to the side.. Or entertaining.. Sometimes I am in a hurry but I always will get to the video later.. At least your videos.. Hopefully you and Al are doing ok.. He took it pretty hard on that car.. Poor Al.. Lol.. He spent so much time on it.. He is a good guy.. I think he let the comments set him off too much tho.. You are gonna have na- sayers.. Life goes on and most of us appreciate.. It is easy to get upset as a viewer in that the suspense leading up to it and this car is sorta personal to us too.. I was pissed at first about Slaghammer but I quickly realized, dude, how you think they feel and it's not even my vehicle.. Lol.. But I was like, Damn it.. Then after a minute I calmed down and felt bad about tbe situation.. And you know, Over all, Al and you guys kicked ass! Made Power Tour, a few runs and then some trouble.. But it happens and in my mind you guy accomplished a mile stone with that car.. It was a crappy 4 door carcus not very long ago.. So I don't care what anyone says, Al kicked ass on that car after working all day and his days off and the man isn't exactly a spring chicken so to have that dedication is remarkable.. You guys need to go have some fun and blow off some steam or something.. Not that you are fighting, idk bout tht, but have a holliday somewhere fun.. Go race go karts or something..lol.. Love you guys! ✌
Thank you
Ditto, great video and great way of explaining it, Uncle Tony. It could have gone even longer and I would still be listening. 👍🏼👍🏼👍🏼
@@UncleTonysGarage Speaking of Power Tour, Thunderhead289 was there with his AMAZING! 45 MPG! V8 Maverick. The problem is it can barely reach highway speeds. He 3D printed an intake to mount up a lawnmower carb, added a home made, electronic air bleeder to continuously tune mixture, and 45 mpgs!
I have trouble understanding it, but I think he also advanced the timing to take advantage of the continuous vacuum, so maybe tons of vacuum advance could combine his mileage with some power? Or should he, or I, try to make another manifold to bolt a big carb up in addition to the lawnmower carb and a staged throttle linkage? or bolt his mower manifold to a dual quad manifold? I think, however, that he would have to then replace his advanced base timing with vacuum advance anyway.
So can anyone out there help me understand his amazing results so we can then use that understanding to combine those results with more normal power? or even high power?
@@alan6832 I think if you restrict the power output of the engine that much, and do it efficiently, those kind of mileage numbers are going to be achievable no matter how you do it. That's the only reason it worked. If you changed the setup for a "power on demand" with a separate carb and everything, it would end up being the same as just running something like spread bore or an EFI setup. Only way you get 45 mpg out of that is to keep your foot out of it. This is not to mention that his test was all highway miles on flat ground. Most well-tuned engines will have surprisingly high cruising mpg. It's the acceleration events that use all of it. With thunderhead289's limited testing, not only was it highway miles, he also made it impossible to use a lot of fuel under acceleration. Hope that makes sense.
An easy way to tell if you have too small of a carb is when your floor it and both secondaries are open and your still pulling a vacuum ( typically with a vacuum gauge routed in the vehicle) of 1 or 2 inches of vacuum or more you know is a good indication of a carb that’s too small!
If you have 1 inch of vacuum at the top of the rev range with 0 in the mid rev range you have the right size carburetor. Thats for the street use in my opinion. Always better to go smaller than bigger on the road
1 inch is fine, ya need some vacuum. If 3 or 4 inches, feel free to go up in size.
Good point.
Makes tons of sense and I guess would explain somewhat the performance of modern cars. Because they can build huge CFM capability into the intake tract and the computer makes it work in all conditions.
Many years back, I'm thinking about1978-79, I built a 318, Edelbrock LD-4B, milled the heads, headers, 268*/.450" cam, cool stuff. I got a great price, $80 on a new Thermoquad from Direct Connection. Got the spreadbore adapter. But it would bog big time off the line. Thought it was too big for the engine. Traded it off for a used AFB which I rebuilt. No bog, but I could tell I had lost power in the mid to high RPM range. I did not know at that time how to adjust the air valve on a Thermoquad. Those were the days of no internet, and I didn't have a clue how to find out, or what was really the cause of the bog. I know now the Thermoquad was used successfully on 318's, without the bog, even though it was somewhat larger CFM than the AFB. Live and learn.
I had a built 355 68' Camaro Street/Strip. I tried a 750 and it didn't work. I didn't know a lot and It had a stock converter. The wife had to drive it to work every day and I needed it to run good for her too. So I went to Super Shops and bought a new 600 vac secondaries Holly. The thing ran like a dream out of the box. No top end though. So I put a Nos plate under that 600 for when I would go race people. Tires were shit back then. It would launch great on the 600 but white smoke if I left on the squeeze. I had to wait till 2nd engaged to hit the NOS. My point is, you have to consider the converter also. And the rear gear ratio. Along with the weight. Auto or manual. Even tire size. I kick myself in the ass all the time for selling that car so I could buy the New GSXR that just came out a year or so before. A little cam advance and I never lost a race on that thing. It was lightyears ahead of anything else that was out in 87/88 whenever it was. Then i had no remorse. Now I wish I had that Camaro.
I like to experiment.My trailer-dragging,junkyard hoisting Dawg has a mild 390,headers,electronic ignition,C6,3.73 gears, and a big honking tunnel ram with a pair of 500 cfm 2 barrels.Gets 22 mpg.Got 16 with a '75 Mercury sled on the trailer.Up next,2 32/36 Holleys on my 200 six
Recently found Tony 's channel and I'm quickly becoming addicted to watching every video! Endless amount of knowledge and no BS
I really enjoying when you talking about carburetors, I can watch you talking for hours because you really know what are you talking about!! Please do more of those carb videos cause there are many useful small information on these videos that makes huge changes on performance engines.
I for one, can never get enough of your carb videos. Keep it up.
I never claimed to know Tenth of what Tony has provided me with since I subscribed.
You sir are "The Man".
I raced a 1967 Mustang with a Factory 289 and factory 4 barrel intake. 4150 if I remember right. That car ran like a banshee and ate a lot of small blocks' lunch.
I made a decent living off my wins on 2 lane back road raceways. Small tuning on that factory carb was priceless.
Thanks for the knowledge Uncle Tony!!!
nobody who wants to learn dropped off early uncle tony ,your real students stayed the whole 20 plus minutes. and thank you for the chance to learn great video
The old holley 780 cfm carbs were hard to beat can't understand why they quit making them would love to find one in good rebuilding condition great video brings back memories stop light to light racing
Is that the 3310?
I agree Danny, best carb The 3310 Chevy only I believe, downleg boosters and a metering block you can jet. You can get 3310s but most have plates like a 600. Back in my youth, you could find a Chevy 3310GM carb but you don’t have the kickdown stuff for a Ford, they might work with a 727, I don’t know. All of my Mustangs had 3 pedals and downleg metering block 3310s even a 289 that would turn 8000. I put a 11inch 3 finger in it with a 70 1/2 351C 4V closed chamber Falcon that when I went out of town a few months my buddy didn’t drain the water and put anti freeze and cracked the block. Cleveland’s would run but the block was made of bread dough. Anyway I had a Chevy 3310 carb on that Cleveland. Ran really good. But 2nd best is a 3310 straight boosters and put a metering block on it, an adjustable secondary pot and mangle modify the bracket to allow the secondary to work well. Take it out on the road and romp it and adjust the pot to just on the edge before it bogs, and make sure the blades fully close. If you can grab the link under the diaphragm and close it even a hair go to the next spring. I have the long yellow in mine. Take it to the strip and run an 1/8th mile. Write it down as a base line. If you feel like you didn’t get a good start do three assuming it is test and tune. Then try 2 sizes lean at a time until you slow down then go back to the base and see if you are faster after a few runs, the go two at a time until you slow down if you go faster more than you went lean split the difference between fat and lean and you should be about right. Do the same with the primary side and do the same thing. Adjust your idle with a vacuum gauge to the highest steady vacuum and fatten it 1/16 turn. Change plugs and make a couple of good runs and you should post your best run. I like an o2 sensor and a vacuum gauge for the PV. A mild cam you may need an 85, if it puffing black smoke I have run 35. The main thing is that if you gag it you shouldn’t get a pop(Lean) or a sag bog with black smoke (Rich) When you go to the stoplights, you’ll be well prepared.
The old 780 3310 is the same as the newer 3310 other than......the old one has dogleg boosters which do add the extra CFM. I have a SuperFlow 110 and when I flow a straight leg 3310 with the choke tower still on, they're around 750....when I knock them out and install the dog leg or the double step dog legs, they go up at least 30 CFM....some go over 800.
The older 3310 is also a 4150 which has a jet plate on the Pri & Sec......the newer one is a 4160 which means in has a jet plate on the pri side and a metering plate inside the sec float bowl.
The type of bowl....center hung vs side hung has nothing to do with the style.....4150 vs 4160 as there are 4160 750 & 780's as well as 600 CFM 4150 (early 1849 & 1850) as well as the billions of 600 CFM carbs that are 4160.
Simply put......4150 = 2 jet plates 4160 = 1 jet plate I make a conversion for the sec metering plate so you can use standard Holley jets instead of changing them or drilling the main orifice.
The early 3310 also had a Ford style hot air choke which became a hand choke in the mid 70's. 3310 -2 as I recall is the choke change. Holley also had a hot air choke on the 1850 until the same time. I have an 1850 in my core supply a customer bought new about 74 he gave me that has the hot air choke I converted to electric and still has the original sec jet plate. It went on his 302 Mustang
The reason Holley stopped making certain models or, more accurately, changed them is $$$$$. It's cheaper to remove things, eliminate machining operations than develop a new model from scratch.
@@patrickrodig5667 Downleg boosters, dogleg boosters are worse than straight ones.
I have an old 3310 sitting on the shelf. I picked it up probably 30 years ago. I'll have to check to see how it is set up. I was young at the time and haven't looked at in in probably 25 years..
I always went by airflow. The more airflow you have front carb to rear exhaust, This will give you the most power. Hence the bigger carb. I run a 750 Holley double pumper 4 corner idle on a stock Chevy 350 with a mild cam stock heads 2 inch headers to a 3 inch collector with 3 inch pipes to 3 inch in and out mufflers and this motor runs like crazy.
We found great success on Datsun L20Bs(approx 120 cubic inch 4 cylinder) by putting 2 barrel ADM Weber from 250 cubic inch 6 cylinder Ford Falcon, almost equates to what you said about doubling.
I had a 1300 datsun, cam in block.
Thank you for this video!! Awesome information. This is hands down the best channel on RUclips.
Awesome real word info, me and my brother have been tinkering with hot rods all are lives, every time i watch a video from UTG i learn something new.
Excellent, thanks. I saw this with two-stroke dirt bike engines, in the 1970s. In about ~1974, a stock 125cc motocross engine might come with a 26mm or maybe a 28mm carb. Then, one of the mags did an article about a tuner who was putting _huge_ carbs on them, like 36mm or 38mm -- bigger than the mightiest factory 400cc+ bikes! Everyone said, _This thing shouldn't even start..._
But it worked really well for racing and high-performance operation. Power, response, area under the curve, the whole thing. The factories started putting far bigger carbs on their hottest engines almost immediately. It swept the industry in basically one design cycle. Wish I could remember the tuner guy's name.
My bone stock 66Chevy Caprice 396, 325hp absolutely LOVES the Eddy 600cfm
1406 carb. Absolutely no bog or hesitation when I slam it from a dead stop, she just eats and spins that one wheel peel on the 12 bolt, 2:73 rear gears. I had to fatten it up quite a bit, rods in the primaries, jets in the secondaries. Took about 20 minutes and didn’t spill a drop of fuel. Love those Edelbrock carbs. She’s a cruiser so it’s the perfect setup. 👍
Your combo sounds like you are correct.
I love your videos man, grew up workin on cars with my dad and grandpa and now I have my own classic cars that I love working on. All this knowledge is golden and unfortunately being lost. Thank you for passing it on to the newer generation with your videos!
Another thing people forget… the reason that they rate 2 barrels differently is because they have a higher signal because less surface area exposed to vacuum. So the rates cfm decreases when you have a more surface area. If you’re running two 500cfm holleys that’s closer to running 1 850cfm
@Burned Out Garage, the vacuum signal that people refer to when talking about carburetion, is the amount of vacuum produced at the throat venturis and the boost venturis (aka-Ported vacuum)..... It sounds like the"'exposed" vacuum that you might be thinking of (?) might be the manifold vacuum (aka-MAP)... As the throttle is opened, the amount of manifold vacuum decreases, while the amount of vacuum signal in the venturis increase.... This is because the air velocity increase in the venturis will increase the vacuum in those places in the carburetor. But the increased amount of ambient (outside air) air volume being allowed to enter into the intake manifold, will decrease the amount of vacuum in that area.... The greater velocity through the carb. Venturi's will produce large vacuum signals, which is why the lower CFM carbs like typical 2bbl. units, typically respond so well at lower rpm's ... The reason the multiple 2- bbl carb set-up's gave less bog than the large cfm mech. secondary 4-bbl carbs is because the center carb would open first with the driver command, then as the vacuum signal of that carb's venturi's increased as the rpm's increased, the fwd and aft (vacuum signal operated) carbs would smoothly start opening up... That is what made the multi 2-bbl carbs so drive-able. Smooth - but accurate application of the outboard (forward and rear) multiple throttle butterflies.... A brilliant design.... No computers , sensors, injectors, wiring, connectors, relays, fuses, electric fuel pumps, fuel pressure regulators, multiple fuel lines, or high (70 psi) fuel pressures involved with these designs, that the modern F.I. engines rely so heavily upon... Just innovative engineering and the laws of nature (Bernoulli's Law). Simple , yet effective designs....
Something to be said for stronger vacuum signal, therefore snappier low speed throttle response, with a smaller carb.
If i recall correctly, 2bbl carbs are flowed with 3" of vacuum and 4bbls are flowed at 1.5" of vacuum...can't recall if it's inches of water or mercury.
@@michaelmartinez1345 yes exactly; Bernoulli’s principal describes the reason 2 barrel and 4 barrel carbs are rated differently. Pressure decreases when the area of restriction increases. Because there’s technically not a vacuum, there is just less air pressure then atmospheric, so it’s literally the weight of the atmosphere pushing the air in. It pushes harder on 2 barrels of equal size then a 4. Super interesting stuff.
Well you explained that great often wondered about that
American carburetors have always been a mystery to me. The SU carburetor is the only carburetor system that made sense.
Your videos have really helped me get a better understanding of downdraft carburetors and their functions. It’s understandable how so many great mechanics still struggle with proper sizing and tuning.
Im still clueless. But I feel a little more comfortable after watching each of videos.
Keep ‘em coming!
Amusing. SU carburetors are universally mocked for their ineffective dribbling performance. But for tiny engines with no power, they are fine.
@@oldmusher depends on the SU Size. 50mm + SU’s are pretty darn awesome. The beauty of the SU Carb is they can tuned to provide optimal performance across the entire RPM range. Where American style carbs can not.
The trick is to use the appropriate sized and quantity of SU and an intake flows well for the application.
The primary limitation is non-flow through heads used by the engines that came with SU’s.
My experience is limited to Datsun / Nissan L-Series Engines. Dyno comparisons show negligible improvement with Tripple Webbers vs tuned SU’s. The tripple webbers only outperform at the top of the RPM curve.
But ya. They’re not capable of feeding and engine greater 3.0L.
Excellent video. Thank you for sharing. The cfm calculator lovers are one of the biggest reasons I left almost all of the car/tuning groups on Facebook. There’s no getting through to those people. They completely ignore the word MINIMUM and swear up and down, that the formula is to calculate the maximum carb cfm😂. I love running into those folks at the track, and watching them disappear in my rear view mirror.
Go big or go home
Great vid! Built a 327 ('67-2 bolt mains) chev in 1975 , ported it like you do, 325hp corvette cam, lifters,valve springs. I used a Holley - double pumper Spreadbore and "Doug Thorley" headers. All shoved into a '59 Chev fleetside. Awesome power!, Sun Machines "dynoed" it at 364hp on a portable dyno at our College. I chose the 650 Spreadbore by 2 x the cubic inces. This helped a lot of my friends decide on their CFMs, too. When you use the veh. for cruising and the "Occasional" stoplight race, THIS is the best formula. Thanks, Tony!
These videos are so informative!! I have a 1968 LA318 with intake and 650 CFM Holley double pumper mechanical secondary and it responds beautifully!!
So i had to finish the vid, and ur "Double the cubes" formula is WAY better than the others, like how my 950 is workin great on my 462......just had to add.....GREAT stuff my brother!!
This episode was like waking up on Saturday morning and watching Kroft cartoon super hour back in the 70's. Great content and information Tone!!!
Thanks Uncle Tony! Everybody says to go low with CFM but you bring up some great points that are indisputable facts. You helped me to make up my mind and dump my 750 dp for an AED Performance 1000 HO on my 496.
Awesome video!!! I can't get enough carb videos!!!
Amused. I was once told, “Take the CID, multiply by 2 and go for the lower end.” I’ve always just tried to match my carburetor to my induction, and to my exhaust flow. Breathe in like you breathe out. Never had a problem.
Yep 2CID = CFM is a good start
The best my old 305 ever ran in my '84 GMC 1500 was with a 390 Holley vacuum secondary.
I ran a 450 cfm Holley factory Ford replacement carb on a 351W for a couple of years that previously ran a 600 cfm carb tuned to application with a wideband o2 gauge. Not a damn bit of power loss between the two. Those smaller carbs definitely have their place on smaller engines and mild daily drivers, they give great response.
Thanks Uncle Tony. I learned something today. Great video. Thanks for sharing.
😊 the world needs more uncle tony. Awesome information. You explain it sooooo good.
I had a somewhat rowdy 350 chevy back in the day, I used a 780 vacuum secondary holley square bore. One of my favorite street carbs once it's tuned right. Stomp the pedal through the floor and let the carb do the work.
I am running three 2 barrel holley's on top of a 351C and it works well. Drivability is good and when it's go time it revs quickly.
I had a 225 slant 6 with a 650 double pumper and the engine loved every bit of it 😀
That seams crazy to me! I have a 650 speed demon double pumper on my built 383 Chev stroker and made 511hp!
What carb would you recommend for max output?
@@jakefriesenjake on a 383 Chevy there got to be 1000 videos of dyno runs with big carbs. The biggest carb always wins WOT on a dyno.
@@kennywhiddon1497 well then put a 250 cfm 2 barrel on it brother....ill drive right by you.
The highest quality guidance is completely appreciated your experience is hands-on and tremendous.
Uncle Tony, with the weighted air door on the secondaries on the Edelbrock carburetor, it has to be sitting in the normal position to function the throttle linkage. If you hold the carb on its side the weight counterbalance moves into a position where the throttle cannot go wide open.
This is why spread bore carbs like the Quadrajet are so good.
780 CFM, Holley vac secondary on my 69 383 Super Bee automatic 280 Isky. Loved it, very responsive. Ramcharger hood scoop package.
Absolutely perfect answer to the classic too big vs too small - Chevy vs Ford age old arguments. I couldn't have explained it better!
Lol, I actually had a 71 stock Pinto and ran a Holley 600 vacuum secondary on it. Surprisingly it ran pretty good! I also ran a 2X4 tunnel ram on a SBC in an Olds 442. It was mildly modified but the throttle response was incredible!
Great piece of wisdom. I didn’t drop off. Thanks for the great memories..,yours and mine!
Buick Stage2 was a dealer installed "in the trunk" option - or over the counter. Only 100 pairs of Stage2 heads were made. I know someone who bout his Buick new and ordered the Stage2 option. Still races it. Also, the "formula' SAYS A 455 CI engine needs a 50 cfm carb. But in 1971 Buick switched to an 800 cfm Quadrajet. They knew......
I ALWAYS GET SOMETHING FROM YOUR VIDS, YOU'VE BEEN THERE AND DONE IT, THAT'S WHY I LIKE YOUR CHANNEL.
That helped much - thanks again, Uncle Tony!
The Z28 302 came with a single 780cfm Holley, the crossram I believe came with a pair of 650cfm mechanical secondary Holley carbs. Your point is still valid tho.
That's nuts! What carb would you recommend for my 383 Chev stroker? It makes 511hp and 492 tq on the dyno.
@@jakefriesenjake if I were building a 500ish hp 383, I'd use a 750 or 780 myself if it was mostly used on the street. 850 if it's for track use.
@@adammcilmoyl4278 strictly street use. I currently have a 650 speed demon double pumper on it. Pulls hard
@@jakefriesenjake it probably does work well, they're a good carb, but a larger one might give you more from 4500 and up.
The other thing to keep in mind too, and I don't remember Tony mentioning this, is that CFM ratings are not standardized or based on actual flow numbers. They are just mathematical formulas, and not all carb manufacturers use the same formulas. It's not uncommon to put a carb on a flow bench and get a number that's significantly different from its rated number. There are lots of chokeless "race" Holley 750s out there that flow well over 800cfm, and some that even under perform too. The Quadrajet is known to flow more than it's rated for, but the Thermoquad typically flows less. The 750cfm "small" TQ actually clocks in around 680-700 on a flow bench, and the "big" 850cfm TQ only really flows about 750-770cfm.
I'm kinda rambling now, but my point is just that the actually cfm rating itself isn't necessarily a meaningful number, and not necessarily comparable between different brands or even different product lines in the same brand (some Holleys are flowed wet, some dry, which produces different flow numbers even on the same carb). If what you have is working for you, that's great, but if you want more up top, something larger might help and might not even hurt low end performance either.
Back in the early 90's used to run chrysler 360 2 barrel carbs on every sbc smog motor I had. I don't have any numbers but it definitely woke em up
Tony , I hear you here .
I have a 1972 Chrysler Charger R/T E37 running a 265 ci Hemi 6 cylinder with a 600 Holley with mechanized secondaries done by me .
Everyone said it is way to big , but mate this 600cfm Holley gave 90% the power of the triple Webbers with 1/2 the fuel economy , great fun tuning this 600 over months , and this was late 90's and your sweet channel was far in the future .
Trial and error was the only way , great fun .
But each of the 45dcoe webers will flow 3-400cfm + so your 600 holley is half roughly the original cfm?
@@guyharrison909 Ain't you listened to a word Uncle Tony has said here ? , it can work both ways ! up and down !
Point taken but mostly tony is saying go for more cfm for performance at the expense of everyday driveability. Have you looked at mirabito performance on RUclips? He shows the difference between 4 barrel downdraught and triple sidedraught on the Chrysler hemi 6. My understanding of the E49 265 was that the webers allowed it to sing at 6000rpm and pull from idle.
Very good info on all your videos , awesome stuff keep it coming
Love the channel, so much good info! Ty Tony and miss tony.
What is maximum performance? My 84 El Camino Super Slow came with a 600 Edlebrock. Complete dog. I installed a 450 quick fuel, and it runs like a scaulded dog😂 It does cute lil one wheel burn outs and third gear pulls hard, all the way. Great MPG, great acceleration, starts on the first bump, every time, runs cool and never loads up during accessive idle. It is still only 200hp, If that. most of my torque is available off idle to 4 grand. for my daily driver, that is fantastic performance😂🇺🇸🇺🇸🇺🇸
For your purposes and engine, that 450 works fine, but I would have tried leaning the Edelbrock down a bit before making the switch. Some Edelbrocks are calibrated very rich from the factory
@@UncleTonysGarage I don't doubt you a bit. I had to weigh my abilities and time😂 If I found your channel a year ago, I may have. Edlebrocks are foreign to me. I know they are generally set it and forget it.
I did put a UT power tune, on it. 1/2 centrifugal lock out, the ol UTG delete a spring trick, and added weight to the advance weights. Runs so good, I like driving now😂 Serious, it runs like a current computor command EFI. All courtesy of this channel❤🚗🚓🚓🚓🇺🇸😂
built a 454 chevy and put in a 1976 camaro. tunnel ram and 2 street brawler 600 cfm... dumped fuel.....first oil change was 90 %gas down jetted 2 X and finally got it , the timing and valves right.. have to have an 1100 idle so as not to be so rich at idle have a 700r4 and at cruise she runs great well at all levels she runs great but she wants to run plain and simple. great video wish i would have seen this before hand. she runs like a dream with all sweat and tears an struggles great videos watch all of them and learn alot all you do is helpful on all makes!!! keep rolling!! ill keep watching!!!
Really like your carb break downs.
This is great info, I actually think I was close to coming to this conclusion myself when doing 'the' carb size calculation and seeing what fast cars were actually running.
Fascinating all the way through. No flies dropped off, I bet. Good topic, Tonester.
Having a rare engine to get horsepower (345 international) forms said never go bigger then stock but mine being hand ported and a 260 cam I got a 500cfm Holley. way more top end and response
I know EFI on many levels is and can be different, but there are things that stay the same too. My friend and I were told repeatedly when building his engine for his Acura Integra that a 70mm throttle body, ported high flow intake manifold, 4-1 header with 2.5 inch exhaust from the collector back, 12.5:1 compression, ported VTEC head, stock cams, light weight flywheel and racing clutch couldn't and wouldn't work on the street. But, said friend daily drives his 1993 Acura Integra and all it took was some driving around and tuning for part throttle. When he keeps his foot light, he averages about 28-33 miles per gallon (which is what the car got stock) but now the car also makes at least 60 horsepower more at the crank than it did stock. And while that may not sound like a huge increase in power for V8 guys with that kind of work....that is at least 60HP on stock cams, from a 4 cylinder engine with only 1.8 liters of displacement. And 200HP in a sub 2,400 pound car is way more fun than people give credit for. I have never given into the carb/throttle body size formula thing, it is all about the tuning and how efficient the engine can use the air it has access to.
Great video. I had a turbo Buick 3.8 in a Chevy Luv, and installed a large carb off a ~'70 buick 455. I was universally informed that it would run poorly and be difficult to drive and wouldn't really help the performance. Initially drivability was poor but with plenty of tinkering, it became very drivable and smooth for normal use, and perceived significant torque increase at very high RPM. Generally I had to get the very low flow mixture dialed in for normal drivability, and elevated fuel flow for the secondaries (no intercooler on that engine). The biggest problem I had was wastegate over-ride and resulting detonation, which took some gas pedal skill to manage.
Great stuff, definitely want more!
I really learned a lot from this video. I really appreciate you sharing your knowledge with us. I have a built 350 that I didn't build. I assume it's 383? It was my dad's car. Before this video, I was impressed with the 600 CFM Edelbrock that it has. After hearing what you said I believe it's starving. I just got it running and it needs to be tuned. But I think it's starving. It's a strong daily driver though. For now I'm going to say that carburetor is keeping me from blowing up the engine. Thanks again brother.
Love it. I learn so much from your videos
Great info and very useable
Thanks Tony
Uncle Tony, you mentioned people dropping off the channel. I could have listened for another hour. listening to someone, who obviously knows what he is talking about, is not what bores me at all. You explained things so anyone should understand. As my grandfather used to say, the day you stop learning is the day they put the screws in your coffin.
Terry from Australia.
Thanks Tony, Keep it going!
Dad had a 67 Galaxy 289 500cc 2 BBL Holley and was perfect!
I agree with Tony, I have two Quadrajets on 310 cubic inches, it took some tuning but now runs fine.
Learned about this back in the day. Had an old 240z that had a few bolt ons, but the stock carbs. Ran and drove good, but wasn’t very fast. Ended up putting on a pair of Webbers with intakes I ported. Ran awesome at higher rpm, but would bog if you were to aggressive on the throttle at low rpm.
With modern stuff many engines have a much bigger throttle body than a similar engine from years ago. But, with the electric throttles the computer rolls into the throttle even if you punch it. That way it still responds good, but also doesn’t give up the high end power.
right now my engine is grannie tuned for gentle gas mileage. a quick carb swap makes my motorhome an overgrown chevelle SS. I only use quadrajets. My favorite carburetor since I was a teenager. My first motorhome was plagued with cooling system issues. after I had replaced the waterpump and hoses, what I thought was a blown head gasket turned out to be a cracked head. I picked up a set of heads from a performance shop at a decent price. Before I installed the heads, I ported the heads. I went as far as drilling the valve guides and making the bowls larger. I also deshrouded the valve bowls to match the diameter of the valve seats. I achieved a redline close to 6000rpms in a 350 small block chevy in a 21ft motorhome! This beast was a traffic monster. I also got into a few road rage chases where the other drivers were shocked that they couldn't get away from me! I destroyed the transmission and later had a modified rebuild on the transmission. My biggest error was that I had just a little too much timing advance and detonated the engine which snapped the crankshaft and I ruined the engine. It was still rebuildable. I didn't wreck the block. I could have done an engine swap for a few hundred bucks and been good to go again. I decided to get a bigger motorhome so I junked the 21ft. I kept the quadrajet from the 21ft and have it as a spare carb for my class A motorhome. I have tried out my 454 with the bigger carburetor setup and it performs well. But it's a pig on gas. I swapped back to the stock carb and run it gentle. I've run spread bore carburetors for over 3 decades. I used to have a couple of carburetor manuals that also showed how to change the settings and specs for track racing and drag racing. I had learned how to get the lean bog out of quadrajets and I make street sleepers that hardly anyone in this day and age even know about. I have occasionally played around with aftermarket edelbrock carburetors on other people's vehicles. But I never could make them perform in any way that ever impressed me. I have no experience with holleys or other brands of factory carburetors (I can't stand ford junk) I've stayed with the Rochester Quadrajets since I was a kid. I know these carburetors like the back of my hand. It's been my secret weapon on the streets and no square bore could even come close to it!
The long theory videos are my favorites
That's a fact Tony, '71 Toreno two barrel cam and heads. I advanced the cam added cheap Herman headers through on a unported Single Plain Dominator and a 800 Thermo Quad stock C-4 trans and factory gear ⚙️. I was lifting the front tires and never bawged down.
Hi uncle tony great video I remember those days that the mopars really ran good. I’m 74 years old I like everything back in the day with all the muscle cars 👍
Nice listening to you. You're spot on. I still love the 850 q jet. Have to meet you for a dinner sometime.
I watched till the end lol truly appreciate the breskdown
Uncle Tony great videos, I enjoy watching and I have learned a lot from your videos. I was wondering if you will be doing a video on rebuilding an automatic transmission. I have seen your engine rebuilds videos. Maybe you have done an automatic transmission rebuild and I just missed it.
I built a 455 olds in a jet boat, put 2 660 center squirters on a offenhauser tunnel ram, 1 to 1 linkage. Old street rod fella at the auto parts store said No way when I told him what I was up to. My father thought the same thing. I started that thing up and set timing. They could not believe how quick and responsive that motor was. Great videos UTG.
Alot of good points there. Thanks Tony.
Awsome info Unk !!!
....Just a point on the outboards on the 6pack. Compare the throttle bores on the standard 500 holley....The 6pack 500s are a 4 barrel rated
Carbs were such a mystery back in the day. I think it helped if you were like my family where we didn't stay locked in to one brand of car. We had at any given time at least 2 different GM cars, a ford and occasionally a pentastar brand. Small blocks and big blocks. After a while we didn't even bother to use the engine books for the engines. We just had "formulas" in our heads and threw parts at each engine based on what we wanted the car to do. My biggest surprise was when I slapped a 600 cfm holley with vacuum secondaries on a 460 engine I had in a 77 LTD. The engine was mildly built and was a torque monster. I didn't have any money left after the build to get a 750 double pumper like I wanted. I had a used 600 on a shelf that already had the Ford specific kick-down linkage so I used that instead.
The car went through left rear tires like a bum went through a bottle of Ripple. And on the highway it cruised at 90+ mph all day with no strain. The engine just WORKED with that carb on it. Big heavy car, big air gulping engine and that "little" carb on top was somehow the perfect combo. Would it have worked better with the 750 double pumper? I don't know. I had so much fun with the 600 I never felt the need to change.
I had a 71 Cutlass with a stock 350/350 turbo. It came factor with a 750 carburetor. That thing never gave me any problems. It ran great and had decent power.
Recently a 80’s t- bird called the bird of prey with a turbo 2.3 did 7.06 at 191 mph in the 1/4 pretty crazy considering the old engine design
@@brracing7861 I still see em almost daily on generators,what a great industrial engine.
Around the late 90s or 2000s they increased it to a 2.5.
People go crazy fast on the old single cam Toyota 3TC motors to
Great video. Real good info.
Awesome video I swear it sounds like you have been answering the last four questions I asked about carburetors LOL right on Tony. Glad to hear all this as I ordered a 650 CFM carburetor to replace the 600 last night. Now I'm wondering if I should have went bigger lol.
Great info. Tony. Thanks