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.

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.

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 ONLY.

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

Accessory Belt = 760K6
A/C Belt = 378K4