Originally, Mustangs used paper-element air filters. But you can get better filtration and air-flow today with a high-performance replacement FilterCharger from K&N Engineering. Consisting of four to six sheets of cotton gauze layered between two sheets of aluminum wire mesh, the filter media is then pleated and oiled to enhance its filtering capabilities and overall performance. Washable and reusable, the FilterChargers are custom designed to fit into existing air cleaners. OE replacement air filters generally add 1-4 horsepower. Also shown is the K&N air filter top, which adds to the air-flow capacity.