Here are a couple of articles on CFM:

http://www.thecarburetorshop.com/Carbshop_carbsizesandCFM.htm

http://www.thecarburetorshop.com/Carburetorsizeselection.htm

For a mild street engines with square bore carb, 400 CFM for a 283, and 500~600 for a 327.

With the spread-bore design, larger carbs could be used due to the small primaries. The early Q-Jets were about 750 CFM.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
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