Some years ago I faced the same challenge.
I made my own filters from some SS screening from Mcmaster Carr, two Summit/Speedway funnel air cleaners (cut up for parts) and some 1/4" high flow racing air filter foam from Pegasus Racing.
As close to 100% air flow as you are going to get.
Here are a couple of pics. Look for my old posts with more pics or I could e-mail you the pics and info.
Cheers
Greg
