Thread: correct formula for carbs

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A question that keeps popping up is the formula to figure the correct carb for your engine. Tne simple formula is displacementxmax engine speed divided by 3,456. Now take a average sbc chevy engine say a 327 and say the max rpm is around 5500rpm's Take this 327x5500 divided by 3456 and it equals 520 cfm. Now you see alot of 327 running dual 4 barrels of 500 cfm with no problem. Is this formula for a bone stock engine? Now you take that same 327 and put better heads, more aggresive cam with new valve springs and lifters, add headers you now have a much better breathing engine which could take dual 4 barrels. How is this formula worked out?

Another scenerio, take my 305. Stock it ran good with a 500 cfm carb. Bored .o6o over to 315 I put a 600 cfm on it and it ran better. Using the standard formula the 305 shouldn't take a carb bigger than 500, but with the more cubic inches only it ran better with the larger carb. Now add headers, a more aggresive cam, better heads, etc. I should be able to run dual 500 cfm 4 barrels with no problem, right? Any thoughts?

2200 CFM, 500 CID, 9000 RPM = 166 mph @8.13.