Crank pulleys, attached to the outside of the crankshaft, are the source of power for a car's accessories. The alternator, power steering, water pump, and air conditioner are all belt driven units, attached to the crank pulley, that use horsepower from an engine to provide their own services. Underdrive pulley systems increase an engine's horsepower by reducing the power required to drive the external engine accessories. By replacing factory pulleys with carefully resized units, the accessories are slowed enough so that their performance does not suffer, but just enough so that more horsepower is sent to the wheels and put to the ground. Where horsepower should be!

Normally, underdrive pulleys like the units found at NonStopTuning will increase engine output by 8 to 15 horsepower! This increase results in quarter-mile time improvements of .2 to .25 seconds, easily making this modification one of the best "bang for your buck" modifications for any sport compact car or truck.

Another great benefit in replacing factory pulleys with underdrive units is reduced weight. Factory units, also referred to as OEM, are generally constructed from steel or cast iron. Pulley systems like those found at NST are constructed of aircraft quality aluminum, making them extremely durable while at the same time much lighter than their steel counterparts. This weight reduction results in less rotating mass on the engine's crankshaft which drastically increases the engine's ability to rev up to speed more quickly.