This unit features dual mandrel-bent tubing with a diameter of 2.75", 70mm. It utilizes polished 304 stainless steel and has a crossover pipe to equalize pressure on both banks of the exhaust. aFe found 11 hp and 10 ft/lbs of torque at the wheels on their test 335i. As an added bonus each system also  includes an aFe drop in air filter, part number 30-10156.