The Mach 2 is designed specifically to bolt straight onto all late model Subaru WRXs and STis from MY01 (MY02 in the U.S.) with no adaptors, extras or modifications required.
This valve is for those who want maximum noise! A large single trumpet and the omission of the plumb back option means that the MACH 2 is loud, efficient, and more affordable than the WRX Hybrid model.
It is a little known fact that the late-model WRX factory blow-off valve is actually designed to leak at boost pressures exceeding the factory level. Replacing it noticeably improves throttle response, and is definitely recommended in applications where the boost has been raised.