Two-barrel vs. Four-barrel CFM Ratings

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dibbons

dibbons

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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.
 
Beats me! All I know is a 6 pack flows approx. 955 cfm. WHEW! I'm done!
 
Never heard that. Flow is flow. Velocity is velocity.
 
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
 
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.
 
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.
 
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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