Ok, I now the general rule of thumb for calculating cfm is 2 cfm per cid rule. And, yes there are variations based on your particular engine-it ain't perfect, just a rule of thumb.

But what if you have different type engines each displacing 305 ci (or 5.0 liters): a v6, v8, v10, and v12. That figures to be around 610 cfm under the rule, but it seems each will have significantly different needs with the v6 having to fill less cylinders of over 50 ci, and the v12 only around 25 ci(just using the extremes as an example). It seems like that should be a factor, is it?

 

It seems like that should be a factor, is it?

Not really. The factors are motor size, filling efficiency and intended rpm range. The type of motor will affect VE and rpm range, so they are indirectly factors for flow requirements, but not just because it's a different motor layout -- it's about head configuration.

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