First, this is born out of a "mental exercise" between the parts boys\nand myself...about the merits of K&N air filter...filtering efficiency\nwithstanding, they are being marketed on the sole concept of CFM at the\nlocal parts store.\n\nHow would one figure the CFM required at some RPM for an "X" liter\nmotor?\n\nWould it consume "X" Liters every 2 revolutions? (4 stroke,\nup/down/up/down - so one time it goes down it will be due to the\ncombustion stroke not intake...right?)\n\nIf:\n1 liter = 0.0353 ft^3 (man, can't imagine cramming 30, 2 liter\nbottles in a 1 foot cube box!)\n\nSo would this be correct? (Liter) * (RPM)/2 *(0.0353) = CFM\n\nFor a 2.3 liter motor with a Red Line of 8000 RPM:\n(2.3)*(8000/2)*(0.0353) = 325 CFM\n\nJust trying to determine if anyone really needs a K&N air filter that\nclaims 450 CFM (in this case) - especially since most people don't\ngenerally drive around at the Red Line!!!