Testing: Up to 31% increase in Flow. 14" Muffler: This system incorporates a large 14" stainless steel muffler which produces a mellow sound while virtually eliminating exhaust drone. Flow and Performance: This MACH Force-Xp cat-back exhaust system is constructed of 2-1/2" mandrel bent 304 stainless steel tubing for maximum flow. Smooth transition bends allow for low turbulence, increasing horsepower and torque. Retains Rear Catalytic Converter: The rear cat is retained on this system to maintain a smooth deep sound but more importantly to keep the system street legal. Dual 3-1/2" Polished Center Exit Tips: Finishing off the exhaust are dual 3-1/2" polished stainless steel tips with laser-etched aFe power logos for an aggressive style. MACH Force-Xp Stainless Steel Cat-Back Exhaust System w/ Polished Tip MINI Cooper S (F56) 14-19 I4-2.0L (t) MINI Cooper S (F56) 14-18 I4-2.0L (t)