ASP 2001-04 Mustang V6 Harmonic Balancer Crank Pulley.

25% reduction Underdrive pulley systems increase engine horsepower by reducing the amount of power required to drive external engine accessories. For example, the alternator, power steering, water pump and air compressor rob horsepower from the engine. By replacing factory-sized crank and accessory drive pulleys with a resized pulley, the accessories are slowed, resulting in more horsepower available to the drive wheels. Typically, a set of Auto Specialties street pulleys will increase horsepower by 9-10 rwhp, and increase mileage. All pulleys are manufactured from Billet Steel or Aluminum, exceeding factory quality.