Add power, sound and unique style to your BMW X5X6 M with this aFe Power cat - back system which produced gains of up to 15 horsepower and 23 lbs. x ft. torque as measured on our in - house dyno. Dual 3 to 2 - 12 mandrel - bent, TIG welded, brush finished 304 stainless steel tubing keeps exhaust flowing smoothly for power gains you can feel. The factory exhaust valve motor is used to regulate the exhaust flow from a closed - valve, aggressive tone to wide - open, competition sound.