War Emergency Power (WEP) is an American term for the throttle setting on some World War II military aircraft engines. For use in emergency situations, it produced more than 100% of the engine's normal rated power for a limited amount of time, often about five minutes.
Maximum normal power would be limited by a mechanical stop, for instance a wire across the throttle lever slot, but a more forceful push would break the wire allowing extra power. In normal service, the P-51H Mustang was rated at 1,380 hp, but WEP would deliver up to 2,218 hp. The Vought F4U Corsair, not originally equipped for WEP, later boasted a power increase of up to 410 hp (17%) when WEP was engaged. Several methods were used to boost engine power by manufacturers, including water injection and methanol-water injection. Some earlier engines simply allowed the throttle to open wider than normal, allowing more air to flow through the intake. All WEP methods result in greater-than-usual stresses on the engine, and correspond to a reduced engine lifetime. For some airplanes, such as the P-51, use of WEP required the plane to be grounded after landing and the engine torn down and inspected for damage before returning to the air.
The German MW50 system required additional piping, as well as a storage tank, increasing the aircraft's overall weight. Like other boost techniques, MW50 was restricted by capacity and engine temperatures and could only be used for a limited time. The GM 1 nitrous oxide injection system, also used by the Luftwaffe, provided extreme power benefits of 25 to 30 percent but required cooling on the ground and added significant weight.
