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Try this,
There is a formula that will get you very close to the proper cfm for your engine. The formula goes like this:
cubic displacement divided by 2 (ex: 351=175.5)
maximum rpm divided by 1728 (ex: 6000 rpm=3.47)
multiply those two figuires (ex: 175.5 x 3.47=608.98 cfm)
Hold on we are not done. You now have to factor in volumetric efficiency. A Nascar race engine runs at 85%-90% volumetric efficiency. A normal street car wil be 75-80%, depending on what you have done with your heads and exhaust.
Ex: 608.98 x 75%=456.74cfm
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