Designed to slow down the power steering pump to prevent it from overheating in racing conditions, this pulley will quickly pay for itself by not just saving your pump, but also your weekend at the track. This pulley is fully balanced and is a 16% reduction. An added benefit is increased power and torque across the entire rpm range the kit comes complete with the crank pulley, tension adjusting tool, and a new crank pulley bolt. fits all 986, 987, 996 and 997 except the turbo, GT3 or dfi. a boss on the front of engine case will need to be cut down slightly to clear the smaller pulley size. Will work with the factory belt in new condition, but a 10mm shorter belt is ideal and recomended. for Boxster or Cayman with ac removed, use ac delco #6k750, or Porsche #996.102.151.65 belt .