The Dinan D660-3950 Free Flow Axle-Back Exhaust is designed for the 2000-2003 BMW M5 E39.

The system uses 304 stainless-steel construction, Dinan Tuned Resonance Chamber Technology and dual 3-inch polished stainless-steel tips. Dinan lists a maximum gain of 6 horsepower and 5 lb-ft of torque when used with software.

The exhaust uses factory brackets and hangers for factory-like fitment and is designed to improve flow while keeping cabin resonance controlled. Dinan classifies it as emission code 5 because it does not affect vehicle emissions.