Blazer,

One method is to use a formula to determine the CFM requirements for your engine. It's based upon the engine's cubic inches and the maximum RPMs that you expect to turn. You also need the VOLUMETRIC EFFICIENCY PERCENTAGE (VE%) of the engine. If an engine could use all of the air it ingested, it would have a VE% of 100%. Some performance engines reach this level. Most production engines and most street performance engines have VE levels below 100%. Stock, production, low performance engines will fall around 75%-85% volumetric efficiency.

The formula is: CARB CFM = Cubic Inches x RPM's / 3,456 x VE%

So, if you can turn 6,000 RPM and your engine has a VE of 95%...

454 x 6,000 / 3,456 x 95% = 749 CFM

You should probably run a 750 or 850 CFM carburetor.

Dan J