A supercharger is a device designed to improve the performance of an internal combustion engine. It uses the motive force produced by the engine (usually taken via a belt from the crankshaft) to increase the pressure of the fuel and air mixture in the intake manifold, and thence in the cylinders. Increased pressure allows the insertion and combustion of additional fuel, which means more power in an engine designed or modified to utilize it. Supercharger performance is usually measured in boost p.s.i. in the English Measurement world. This is the increase in pressure provided by the supercharger over a normally-aspirated engine. (Actually, it may be the increase in intake pressure over ambient.) See also turbocharger.