The Myths And Realities Of Carburetor Sizing- History Proves The Formulas Don't Work

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Published 2022-10-07
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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All Comments (21)
  • @Twogreenfeet
    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!
  • @KJ_Moore
    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!
  • @BPattB
    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
  • 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.
  • @guyjordan8201
    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.
  • @mdcuddy3286
    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!
  • 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. 👍
  • @Anthony-vq1wn
    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.
  • @2HacksGarage
    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.
  • 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.
  • @jeremyjc1978
    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
  • 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.
  • @silent1967
    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 !
  • 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 👍
  • @rcberry
    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!
  • 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 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.
  • @markcole6475
    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!
  • @sunnyray7819
    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! ✌