Dinan engineers designed the F33/F36 440i 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. Not only is the tone improved but the additional burbles and pops that come with it are simply intoxicating. Dinan also incorporates a Helmholtz chamber design that reduces resonance or"drone" at low RPM. The system is built to exacting specifications to ensure perfect fit using the factory hangers. It is made from 100% 16 gauge 304 stainless steel and will resist corrosion for years to come. The design features twin 89mm (3.5") polished or cermic black exhaust tips for a tasteful high-performance look. Factory computer controlled exhaust valve is eliminated.