Corky Bell states that a good clean air filter with alot of area and a bell type shape is ideal for turbo charged engines. The main factor here is to reduce the pressure drop from before the filter to after the filter. So you take a vaccuum gauge and messure pressure before and after the filter under load. The ambient air the turbo see's is after the filter, so if you can reduce that pressure drop you reduce turbo heat because it doesnt have to work as hard to make requested boost. This lets you run more boost with less chance of detonation. I think looking for power increases from MAF flow rates is trivial...it's all about the pressure drop and working those KO3's less!

2000 Silver/Onyx Tip S4
Current mods:
Euro Lights,17x8 BBS RC's, RS4 grille, AWE center boost gauge , Borla exhaust
Options:
Bose, Cold weather, Nav, Convenience