600 CFM too small for 400 sbc?

Discussion in 'Engine Topic' started by schevy, Dec 8, 2005.

  1. schevy

    schevy Member

    Sep 29, 2005
    Columbus Ohio
    I`ve been having fuel shortage problems in my 400 and was wondering if it could be the carb. It had a 850 dp on it when I bought it, and I replaced that with Edelbrock Performer 600 CFM. Is this too small? I`m not sure the cam size, but I do know it is oversized.
  2. Eliminator SS

    Eliminator SS Veteran Member Lifetime Gold Member

    Nov 14, 2002
    South East, Nebraska
    CFM of the carb is determined mainly by the CI of the motor.
    Rule of thumb, since the GM plant used 780's on 402ciBB's, LT1 350's, and even 302's. I'd say you should be running atleast a 750.
    Stay away from edelbrock if you want to keep your full power potential. I only use edelbrock stuff on street only mild motors.
    If you want a brand new carb, this is what I recommend (since 780's are few and far between).

    GOSFAST New Member

    May 30, 2005
    Long Island, NY
    Carb Size vs. Cubic Inch

    The carb size has no "direct" relationship (usually) to the cubic inches. We just pulled a 406" SB with 10.9:1 C.R. off the dyno and it wanted nothing less than a 1050 Holley nor anything under a 2.000" primary pipe. It made 580 HP and 523 Ft.Lbs. torque. It does run on 93, however it will be raced on 100 unleaded. It comes down to ALL the combined overall components. Thanks, Gary in N.Y.
  4. Buickfunnycar

    Buickfunnycar Veteran Member Lifetime Gold Member

    Wan't the 800cfm carb used on the '67-9 DZ302's?
  5. Mwilson

    Mwilson Veteran Member

    What are the motor, gear, tranny/converter specs? Most street strip 400 use 750-950 depends on your setup
  6. rustbucket79

    rustbucket79 Veteran Member

    As a lower RPM daily driver your carb is the correct choice, but you will be restricting the HP potential from about 5000 and up.
  7. simso

    simso Veteran Member

    Jul 10, 1999
    Australia Perth WA
    Carb is related to cubic inch size of engine and its also related to rpm, its got nothing to do with cam manifolds CR ect. Example For a 350 engine that you rev out to 5000 rpm then you need a carb with a cfm of 506.36 if you rev it out to 7000rpm then 708.9cfm. As far as compression ratios this has no relation in anyway to carb sizing, you go to high on your compression ratio and you need to run different octane level fuels not bigger carbs. All manufacturers use the standard carburettor sizing formula and its based on max rpm and cubic displacement of engine not compression ratio. A higher compression engine may rev higher than a standard engine but once again this is then the rpm factor of carb sizing
    The only other difference is whether you want vacuum or mechanical secondaries and whether or not you want a double pumper but these extras are all personal preference, not what the engine needs
    Last edited: Dec 8, 2005
  8. Mwilson

    Mwilson Veteran Member

    I can tell you that Ive tried 600-850 on my 350 and 850 hits 6500 much faster almost instantly compared to the 600 slowly reving. If you use those theoretical formulas assuming 100% efficiency then yes a 700 will do but carburation is one place where there is a perfect window rather than a specific cfm 700 might be better for street and efficiency but the 850 sacrifices a little low speed efficiency for WOT get down the track seat of the pant shift as fast as you can fun!
  9. Louich

    Louich Veteran Member

    Mar 8, 2004
    Arthur, Ontario
    i ran a 950 on my 412 and it worked awesome
  10. gmachinz

    gmachinz Veteran Member

    Sep 2, 2004
    Des Moines, IA. USA
    The DZ302 Camaros used a 780-cfm Holley with vacuum secondaries and the cross ram option used two 450 Holleys I believe. -Jabin

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