I did my own calculations.
(( CID x Max RPM ) / 3456 ) * 1.1 = CFM...I use this for the cubic feet.
Then the square area of the filter AND the filter level.
If your filter is very fine, like 5 microns, you are going to need a larger area to allow the same amount of air to flow through.
Then there is the accumulated time to a reduction in flow. If you use an area that equals your calculation, you are going to be at a loss as soon as you pull in air and filter it.
Not sure if this hellps anyone, but it is interesting when you are thinking of putting in cold air intake system.
