.. , Dinan Free Flow Axle Back Exhaust 2012 2016 BMW 328i 428i. 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.