[Birdman]

In Spitfire, Mosquito, La5/7 and FW-190A, for example, the Boost/WEP (default key W) increases the manifold pressure of the engine giving a lot more power. In some planes (late Bf-109 versions, Ki-84 etc) the same key is used to enable Water/Methanol injection, again more power (do not switch the MW-50 in BF-109 on or off at 100+% throttle or you'll ruin the engine). So try to press W while flying different planes and see what happens.