Two-barrel vs. Four-barrel CFM Ratings

Discussion in 'Fuel and Air Systems' started by dibbons, Jan 11, 2019.

  1. dibbons

    dibbons Well-Known Member

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    I read where cfm ratings are calculated using different criteria for two-barrel and four-barrel carbs.

    I wonder is that because it is assumed that the two barrel flows at a higher velocity because of the smaller cross section? Thank you.
     
  2. rumblefish360

    rumblefish360 so close yet so far away

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    Beats me! All I know is a 6 pack flows approx. 955 cfm. WHEW! I'm done!
     
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    • toolmanmike

      toolmanmike FABO Staff Staff Member FABO Gold Member

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      Never heard that. Flow is flow. Velocity is velocity.
       
    • 72Dart6pack

      72Dart6pack Harder Better Faster Stronger.

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      Last edited: Jan 11, 2019
    • 67Dart273

      67Dart273 Well-Known Member

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      Not only are Holley 2bbls rated different than Holley 4bbls, but Carter used to rate theirs different from Holley

      I believe Carter were rated "wet" which was supposed to be more realistic

      Holley 4bls (I believe) are rated at 1.5Hg" vacuum drop where 2bbls are rated a 3" Probably had to do, at the time, with accuracy of testing equipment
       
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      • pishta

        pishta I know I'm right....

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        six packs were rated lower because the draw across 6bbls was weaker than across 2 or even 4 bbls. I think Vizard only rated the 340 six pack at like 780 due to the fact that the smallish 340 just could not pull more air through them. The 440s were rated higher simply because they could pull more. Dont confuse Carbs CFM to what they can pull on your motor. A darn quadrajet will run a slant six nicely cause itll only pull what it can ecen with the larger secondaries as they are variable.
         
      • rumblefish360

        rumblefish360 so close yet so far away

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        Pista, The carb ratings were done by the parent company and have nothing to do with what they sit on.

        To that end, it had my 6 pack ported.
         
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        • crackedback

          crackedback FABO Gold Member FABO Gold Member

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          Take any holley 2 barrel rating and divide by 1.414 and you get the rating at the 4 brl standard/
           
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