aFe MACHForce XP Exhausts Cat-Back BMW F3x B58Aggressive 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 black finish and a stamped aFe power logo. Exhaust Valve: This catback exhaust system incorporates a factory style exhaust valve which uses the factory exhaust valve motor (not included). The valve helps regulate, direct and control