1979-93 Ford Mustang 5.0 Billet Aluminum Serpentine Pulley Set - Machined Ford Mustang 5.0L (1979-1993) Underdrive Pulley Kit. Machined finish billet aluminum 6 groove serpentine crank pulley, water pump pulley, and alternator pulley without cover (nose). The pulleys are CNC-machined from the lightest, most durable materials possible: 6061-T6 aluminum billet. Underdrive pulley systems increase engine horsepower by reducing the amount of power required to drive external engine accessories. A set of CFR pulleys will increase horsepower by 11-15, and increase mileage by 2 to 3 MPG.