Turbocharger - Turbocharging Versus Supercharging

Turbocharging Versus Supercharging

In contrast to turbochargers, superchargers are not powered by exhaust gases but driven by the engine mechanically. Belts, chains, shafts, and gears are common methods of powering a supercharger. A supercharger places a mechanical load on the engine to drive. For example, on the single-stage single-speed supercharged Rolls-Royce Merlin engine, the supercharger uses up about 150 horsepower (110 kW). Yet the benefits outweigh the costs: For that 150 hp (110 kW), the engine generates an additional 400 horsepower, a net gain of 250 hp (190 kW). This is where the principal disadvantage of a supercharger becomes apparent: the internal hardware of the engine must withstand the net power output of the engine, plus the 150 horsepower to drive the supercharger.

In comparison, a turbocharger does not place a direct mechanical load on the engine. It is more efficient because it uses kinetic energy of the exhaust gas to drive the compressor. In contrast to supercharging, the principal disadvantages of turbocharging are back-pressure, heat soak of the intake air and the inefficiencies of the turbine versus direct-drive.

A combination of an exhaust-driven turbocharger and an engine-driven supercharger can mitigate the weaknesses of the other. This technique is called twincharging.