Designed to reduce the horsepower drain and slow down the water moving through the radiator to allow it time to cool, its very important for the higher RPM's we run today. This oversize pulley is 4.2" diameter, earlier cars used a 3.875" wide pulley. Use of a high capacity water pump helps to reduce cavitation in the water jacket, particularly at high RPM, as well as circulating a greater volume of coolant. Further reduction of cavitation is achieved by using a larger diameter water pump pulley CAM6408 on the A-Plus engines but it is necessary to check clearance between the large pulley and the head especially if a lot of material has been machined from the head face as it may foul the pulley.
This is why this 4.2" alloy pulley has been reintroduced which was originally 4.265"