K&N filters

Alternatively you can calculate it yourself =)

CFM for n/a engine
CID x Maximum RPM / 3456

Round filter : Diameter x Height x 6 x 3.14
Flat filter: Length x Width X 6
Tapered filter: ((Bottom Diameter + Top Diameter) /2 ) x Length x 6 x 3.14
Funny shaped filters: You're on your own, lol

Of course a lot of this is theoretical and you have no idea how it will translate into pracicality (e.g., if you use a flat panel filter at the top, like Howard has done, the calculations become questionable because air likes to enter from the sides typically, so will it provide the full benefit, who knows unless you actually flow test it)
 
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