Dinan engineers designed the BMW 328i/428i exhaust to improve exhaust flow by reducing back pressure. resulting in increased power output and a great sporty sound that is civilized when you want it to be, and pleasantly aggressive under hard acceleration. Like all Dinan exhausts our 328i/428i Free Flow Axle-Back Exhaust is engineered to reduce low-RPM drone so the cabin of the vehicle is still intimate and not drowned in an excessively loud tone. The system is built with ease in mind and utilizes a simple bolt-on installation with included mounting hardware. It is made from 100% 16-gauge 304 stainless steel and will resist corrosion for years to come. The design features twin 70 mm ceramic black or polished and laser engraved exhaust tips for a tasteful high-performance look that yields a maximum performance gain of 4 horsepower and 3 ft-lbs of torque. The factory computer-controlled exhaust valve is eliminated.