K&N Engineering Universal Clamp-On Air Filter - Round Tapered 2.75in Flange - Universal pdm_brake-rotors While the stock 1

While the stock 1

High-torque sprung disc with segmented ceramic facings

2004-2020 Subaru STI

Because the hoses and fittings are consolidated

K&N Engineering Universal Clamp-On Air Filter - Round Tapered 2.75in Flange - Universal pdm_brake-rotors While the stock 1K&N XD air filters use a Deep Pile Design, Extra Fine Weave Grade Cotton and alternate geometries for added efficiency and capacity for off road conditions. This extra thick filtering medium provides the increased protection demanded by high dust conditions while continuing to provide the performance necessary to stay in the front of the pack. The XD Cotton medium was developed for the extreme conditions encountered by race teams in the Baja 1000.