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

The term Parasitic Loss is often applied to devices that consume energy from the engine to create more energy for the engine. 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., also rob the system of power. One would not consider running an engine without lubrication such as an oil pump so in this instance the pump is a necessary parasite that consumes at least some power from the engine (its host).

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 lower parasitic loss of the former.

Another common use of the term is where a new or different design reduces parasitic loss. For instance, the use of a dry sump 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.