You want some more power? aFe's Mach Force XP Cat-back exhaust system produces 11.5 HP and 9.5ft/lbs of torque. The Mach Force XP exhaust system is constructed of mandrel bent, polished 304 stainless steel tubing and uses all factory mounting locations for a easy install with no cutting or drilling required. The Mach Force uses a unique 3" resonance chamber to cancel high frequency sound waves producing an aggressive tone on throttle with a smooth sound at cruising speeds resulting in a sporty but not obnoxious tone for your luxury sports car. The elimination of the muffler produces a weight savings of 15lbs! Polished 304 stainless steel dual tips finish off your 135i right.