Auto Specialties underdrive pulley systems increase engine horsepower by reducing the amount of power required to drive external accessories. For example, the alternator, power steering, water pump and air conditioner all 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 drive the rear wheels. Typically, a set of Auto Specialties street pulleys will increase output by 12 to 15 horsepower, resulting in quarter mile time improvements of .2 to .25 seconds. All pulleys are CNC machined from billet steel or aluminum, exceeding factory quality.