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cool formula's


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im tryign to find a air filter big enough to flow for my new needs.


here are some cool formula's


To determine the maximum volume of air your engine will use, take the

displacement in cubic inches and multiply by the maximum RPM you operate

the engine at. If the engine is supercharged or turbocharged, divide

the pounds of boost by 14.7, add 1 to this answer, and multiply this

value by the CIDxRPM value. Divide by 3,456 for a 4 stroke engine, or

1,728 for a two stroke engine. This will calculate the maximum airflow

required by the engine.


Cubic Inch

Displacement x Max RPM x (B) lbs. boost



---------------- +1 = B


3,456 or 1,728



To determine what volume of air a given filter is capable of flowing,

multiply the diameter of the filter by its height, multiply by pi

(3.14), and multiply by 6. If the filter is a tapered cone (different

diameters at each end), add the diameter from the top and base together

and divide by two for an average diameter. Here are some examples:


Round Straight filter:

Round Tapered Filter:

CFM = dia. x height x 3.14 x 6

CFM = (dia. base + dia. top)


---------------------------- x height x 3.14 x 6




i flowed like 1500 cfm's on my engine and i only found one filter for 3.5 pipe so far and its like over 1 foot long so im going to have to bust out the sawza

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