This kit includes an overdrive alternator pulley that is smaller diameter in size to help retain the standard voltage. In addition to the overdrive alternator pulley includes the crank pulley. This is recommended for cars with an automatic transmission and/or a high powered stereo.

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 12-15, and increase mileage by 2 to 3 MPG. All pulleys are manufactured from Billet Steel or Aluminum, exceeding factory quality.

ASP LS1 underdrive pulley kit reduces parasitic power losses associated with high accessory speeds, freeing up additional HP. It also reduces the rotating inertia on the front of the crankshaft allowing for faster revving.ASP LS1 underdrive pulley kit reduces parasitic power losses associated with high accessory speeds, freeing up additional HP. It also reduces the rotating inertia on the front of the crankshaft allowing for faster revving. We have seen just over 13 rear wheel hp increase with this kit installed on stock LS1s.

When replacing the crankshaft pulley on an LS1, a new GM crank bolt is required. This is due to that bolt being a torque-to-yield bolt; meaning that it can only safely be used once. This bolt is sold seperatly and is available in a drop-down menu below if you would like one included with your order.

Also available to help with installation of the crank pulley is the longer crank pulley bolt. Click HERE to read more.

Crank pulley and Alternator Pulley in this kit.

NOTE: New belts are required for this kit. The correct belt sizes for this kit are:

Accessory Belt = 755K6
A/C Belt = 378K4