Superchargers

A supercharger is a mechanically driven blower, geared or belted to the engine crankshaft, that compresses intake air independent of exhaust energy. Early forced-induction engines used them, but the turbocharger, which runs on otherwise wasted exhaust energy, displaced them on marine engines because it costs no shaft power. Mechanical scavenge blowers survive only in niche roles, such as the under-piston pumps and chain-driven blowers of legacy uniflow and loop-scavenged two-strokes, and in the electric auxiliary blowers that assist a two-stroke at low load. The defining trait is the mechanical drive: a supercharger always draws crankshaft power, where a turbocharger does not.