The P2M 63.5mm (2.50") exhaust control valve for all 2 bolt flanged 2.5" exhaust system. The ECV is butterfly regulated to control the exhaust noise for aftermarket exhausts to be discrete while driving on public streets. With the ECV partially open the exhaust noise can be bring down by as much as 50% or more. With the butterfly fully open will bring you back to normal level. This kit is mainly for normally aspirated applications using a standard 2.50" exhaust.