Parasitic loss

In short, Parasitic Loss is a loss that a parasite consumes from its host which may or may not be beneficial to the host.

Parasitic loss in internal combustion engines

In the internal combustion engine almost everything including the driveline causes parasitic loss. Bearings, oil pumps, piston rings, valve springs, flywheels, transmissions, driveshafts, differentials, etc., all are responsible for parasitic loss. One would not consider running an engine without lubrication such as an oil pump so in this instance the oil pump is a necessary parasite that consumes at least some power from the engine (its host).

The Parasitic Loss term is often applied to devices that consume energy from the engine to create more energy for the engine. For instance, a supercharger derives its power from the engine to create more power from the engine. The power that the supercharger consumes is parasitic loss and is usually expressed in horsepower (hp). While the hp that the supercharger consumes in comparison to what it generates is small, the hp is still measurable or calculable.

One of the desirable features of a turbocharger over a supercharger is the turbocharger's lower parasitic loss.

Another common use of the term is where a new or different design reduces parasitic loss. For instance, a dry sump improvement over a wet sump results in lower parasitic loss. The reason may be less friction or many other variables that cause the design to be more efficient.