Aggressive Sound: A free-flowing, transverse muffler is used to absorb high pitch tones producing a powerful sound and unleashing all available horsepower and torque. The muffler is finished with a high-temp powder-coated metallic black finish and a stamped aFe power logo. Exhaust Valve: This axle-back exhaust system incorporates a factory style exhaust valve which uses the factory exhaust valve motor (not included). The valve helps regulate, direct and control the flow of exhaust gases by opening, closing, or partially obstructing passageways depending on throttle position for maximum performance. Simple Installation: This MACH Force-Xp axle-back exhaust system uses factory mounting locations providing stability and a hassle-free installation. Quad 3-1/2" Stainless Steel Tips:Finishing off this system are Quad 3-1/2" diameter, 304 stainles s steel tips with laser-etched aFe POWER logos. Brushed 304 SS Construction: The performance axle-back exhaust system is constructed of 2-1/2" to 3" mandrel-bent, brushed 304 stainless steel tubing for maximum performance, corrosion resistance and strength eliminating cracking. MACH Force-Xp 2-1/2in Stainless Steel Axle Back Exhaust System w/ Polished Tips BMW M3/M4 (F80/82/83) 15-19 L6-3.0L (tt) S55 BMW M3/M4 (F80/82/83) 15-18 L6-3.0L (tt) S55