I'm saying this in the nicest way possible, but please do the world a favor and do not put an aftermarket exhaust on a 318. They do not sound good - at all. Best thing to do is keep the exhaust quiet and focus on handling.
1998 BMW 328is
1966 Pontiac GTO
2007 Subaru Impreza 2.5i 5-door
View my photos: Caught in the Wild