Quote:
Originally Posted by scrapiron
Flat top Ford 2barrel CFM by venturi size --
.98=190
1.01=240
1.02=245
1.08=287
1.14=300
1.21=351
1.23=356
1.33=424
from a HAMB posting some time ago
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One thing to consider on Holley CFM ratings is how they flow rate their carburetors. They flow the 2 bbls at 3.0" Hg (manifold vacuum at wide open throttle), and they flow rate the 4 bbl. carbs at 2.0" Hg at wide open throttle. So the 2 bbls flow a higher CFM rating from Holley. Don't know why they do this other than to make the 2 bbls look like they are more than what they actually are.
Bottom line: A 350 CFM rated Holley 2 bbl. flows significantly less than you think. If a 4 bbl Holley had the same size venturi's and throttle bores as the 350 CFM 2 bbl., it would flow more like 550 to 600 CFM and not 700 CFM like you would think, because it is flowed at a lower manifold vacuum at WOT. I know this can get confusing, but it is based on fact from people I know that worked in Holley's engineering lab years ago. I also have many years of carburetor engineering and flow box experience, so not just talking out of my rear end.
Sal Cicala