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Thread: Calculating Carburetor CFM

  1. #1

    Default Calculating Carburetor CFM

    Hello everyone. So I took a Holley 1850 and milled off the choke horn, then installed thinned primary & secondary throttle shafts along with thin stainless throttle blades. How can I find out approximately how much airflow this this is pulling? Thank you.

  2. #2
    Join Date
    Dec 2009
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    Have it flow tested.
    May God's grace bless you in the Lord Jesus Christ.
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  3. #3
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    Probably not much improvement over a stock 1850 600 Vacuum secondary. What engine is it fitted to?
    And as Danny has already pointed out, have it flow tested. Holley rates their 4 barrels at 1.5 in Hg. Gary
    Regards, Gary

  4. #4

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    Stock 383 Mopar.

  5. #5
    Join Date
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    Default

    Although it's good experience to do all of this to a Holley carb, you'll find little gain with a vacuum controlled secondary carburetor.
    On a 383, it would need to spin to 6000 RPM to flow 600 cfm at 1.5 inHg.
    You need a passenger to observe a manifold vacuum gauge reading at wide open throttle towards your RPM peak.
    If the gauge starts climbing, and reaches 1.5 inHg, then the carb is flowing 600 cfm.
    If the gauge gets to 3 inHg, which I doubt, then the carb would be flowing about 700 cfm.
    If you put this carb on a 632, it could flow 800+, but the engine would be pulling maybe 6 inHg, as the power starts falling off.
    So after your mods, and you have the carb flow tested, it may well have more flow, but will your stock engine pull that additional air?
    Only if the engine can spin higher RPM. Gary
    Regards, Gary

  6. #6

    Default

    Thank you Gary, for the information.

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