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.