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Thread: CFM Ratings & Actual Gas Pumped Through

  1. #1
    Join Date
    Jun 2013
    Portage, Ohio

    Cool CFM Ratings & Actual Gas Pumped Through

    I am doing a little bit of math so I can size my carburetors correctly. The Carb Interactive selector on the site is not helping.
    Let's take for example a 750 CFM Carb, that is 750 Cubic Feet per minute "Wet", the Stoichiometry ratio is ideally 13:1, However EPA Regulated it to 14.7:1. Do these carbs mix at a roughly 13:1 mixture? or a 14.7:1 Mixture? if so that gives me between 57.6 and 51.0 Cubic Feet of Fuel, which is atomized. I could see if someone has the density weight of Fuel when it is atomized.
    More or less what i am doing is some chemistry and thermodynamics to get an approximate horsepower out of my builds before the dyno.
    So my Question is since the rating is per minute, has Holley or anyone done any experiments to see how much fuel is actually dumped in that 1 minute? or any sort of trial along those lines?
    My thought process:
    Let's say that 51 Cubic Feet/minute of fuel weighed 2 lbs/minute (Not even close to the real value, I am just using some numbers)
    I am using turbo blue, the density is 5.90 Lbs/Gallon, -> .338 Gallons/minute. Energy Density is 111,500 Btu/gallon.
    111,500 BTU/gallon * .338 Gallons/minute -> 37687 BTUs/minute, Conversion factor 1 BTU/min / .02358 hp I.
    = approximately 888 HP.
    I <3 math.

  2. #2
    Join Date
    Dec 2009


    Quote Originally Posted by AaronC View Post
    So my Question is since the rating is per minute, has Holley or anyone done any experiments to see how much fuel is actually dumped in that 1 minute?
    If you know your engine's horsepower & BSFC (Brake Specific Fuel Consumption), divide that value by 60,
    and you'll have the pounds of fuel per minute for each horsepower it produces.
    Then you'll need to convert it to whatever unit of measure you need for your equations: (Example)
    Problem is, most people determine their HP & BSFC during the dyno session.

    BSFC reference links:
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & MT 245/45R17 tires.

  3. #3
    Join Date
    Jun 2013
    Portage, Ohio


    Thanks for the input Danny! It looks like we almost have the same taste in vehicles too. Ha Ha!
    I'm going to attempt some tests I guess with the variety of carbs I have, I want to find actual fuel flow.
    Darn Engineering has me thinking ahead!

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