What Is a Supercharger Pulley? Definition, Meaning and Concept

A supercharger pulley is a device used on a supercharger to drive the unit through the use of the engine's accessory belt drive system. Mounted on the end of the supercharger input shaft, the supercharger pulley is designed so that its size is proportional to the speed at which the supercharger rotates, resulting in a predetermined power potential of the unit. By altering the size of the supercharger pulley, the rotational speed of the unit affects the amount of boost or pressure at which the unit will push the fuel mixture into the engine. Most pulleys are made of steel and are designed to work with a pulley-type, grooved, or Gilmore-style belt drive.

A supercharger is nothing more than an air compressor mounted on top of a vehicle's engine. The unit is powered by a belt that surrounds the engine's accessory drive belt and supercharger pulley. In some applications, the drive belt may be unique to the supercharger and run only from the vehicle's crankshaft hub to the supercharger pulley. Commonly an aftermarket type supercharger, factory installed units commonly use the engine's fan belt and are designed not only to serve engine components such as the water pump, alternator and fan, but also to pass around the supercharger pulley.

As the supercharger rotates, it fills the engine's cylinders with a much denser mixture of air and fuel than a traditional fuel system. This allows the engine to produce much more power than a similarly non-supercharged engine package. Engine manufacturers can adjust the amount of power an engine is capable of producing by altering the supercharger pulley size. As with any chain or belt driven component, changing the size of the pulleys or sprockets will change the speed at which the device rotates, thus altering its performance.

The common supercharger pulley is pressed onto the tapered input shaft and secured with a single bolt or nut. The pulley is held in place by the fastener and prevented from turning on the shaft by a key that fits into a slot machined into the shaft and the pulley itself. On some supercharger units, the drive pulley is attached to the input hub by six bolts. On this type of supercharger, often referred to as a root-type blower, the upper and lower drive pulleys are different sizes and are interchangeable, allowing the unit to be overdriven or overdriven. This allows the engine to run at one supercharger gear ratio, and when changing pulleys, a different gear ratio is applied.