This race down pipe uses a unique resonance chamber to capture sound waves and minimize in-cab resonance producing an aggressive tone on throttle with a smooth sound at cruising speeds without effecting performance. In recent testing, the race version down pipe produced +14 horsepower and +39 lbs. x ft. of torque. The high-flowing down pipe is designed using mandrel-bent, 304 stainless steel tubing for optimum flow resulting in added horse power and torque. The down pipe is 100% hand TIG-Welded and uses a 3-1/2" into 4" stepped design that increases exhaust velocity and eliminates low pressure drops which helps to scavenge the exhaust for increased intake charge and more power. Twisted Steel 2-1/2 IN to 3 IN 304 Stainless Steel Street Series Downpipe BMW 335i (E9x) /135i (E82/88) 11-13 L6-3.0L (t) N55 BMW 335i (E9x)/135i (E82/88) 11-13 L6-3.0L (t) N55