First, this is born out of a "mental exercise" between the parts boys and myself...about the merits of K&N air filter...filtering efficiency withstanding, they are being marketed on the sole concept of CFM at the local parts store. How would one figure the CFM required at some RPM for an "X" liter motor? Would it consume "X" Liters every 2 revolutions? (4 stroke, up/down/up/down - so one time it goes down it will be due to the combustion stroke not intake...right?) If: 1 liter = 0.0353 ft^3 (man, can't imagine cramming 30, 2 liter bottles in a 1 foot cube box!) So would this be correct? (Liter) * (RPM)/2 *(0.0353) = CFM For a 2.3 liter motor with a Red Line of 8000 RPM: (2.3)*(8000/2)*(0.0353) = 325 CFM Just trying to determine if anyone really needs a K&N air filter that claims 450 CFM (in this case) - especially since most people don't generally drive around at the Red Line!!!