[vanir]

@ Thighsolater, no MW-50 is a boost system for use under the Full Throttle Height of the engine. Normally you can only use full throttle near the rated altitude of the engine/supercharger fitment (say, typically 5000 metres for a mid-war type) but because the air is thicker below this altitude, if you try to use full throttle and your maximum safe supercharger pressure is 1.42ata, the actual supercharger pressure delivered might be something like 1.7ata and blow the engine. So you have to restrict throttle use (or install a mechanical valve to reduce pilot workload). This is why FTH is a factor when considering aero engines.
MW-50 or some other water-alcohol injection system allows full throttle use and in some cases actually allows further increased supercharger pressures, well below the rated altitude of the engine. So where the throttle setting would cause 1.42ata @ 5000m and say 1.7ata @ 2000m, now you can actually use the full throttle at 2000m anyway without blowing the engine.
This provides overboost and increases the internationally rated output of the engine markedly.

From what I've been able to gather MW-30 might actually be the mixture to allow below full throttle height maximum throttle for German engines. MW-50 includes a more complicated system which also provides a little additional supercharger overboost (say 1.8ata instead of 1.7ata @ 2000m, further increasing low altitude outputs), and was probably designed specifically with the DB-605AS in mind, and then placed in major production as the standard system issued (MW-30 was however also used during the war). I believe Allied water-injection systems are synonymous with MW-30 (although they typically use some other alcohol to prevent the water tank freezing at altitude).

For aircraft which have a maxiumum rated altitude of 8000m like the DB-605AS for example, adding MW-50 gives best performance at around 6800m (or roughly 1-1.5km under the rated altitude of the engine, as modified by supercharger gearing). Water-injection of all kinds is also fantastic for increasing "take off and emergency" engine ratings at sea level (ie. full rich mixture, water injection enabled, gradually open to full throttle for a maximum of 1 minute during the take off run), in order to shorten take offs in field conditions with heavy combat loads.

Full throttle emergency power enabling water injection at altitude should typically only be used for a maximum of 5 or 10 minutes (depending on type) by comparison, before engine overheating and/or catastrophic damage. At least ten minutes of cooling afterwards is required. Water injection systems should only be enabled around 1-1.5km below the normal rated altitude of the engine, simply because the system provides no benefits at any higher altitude than this.

Full throttle should only be used for warbirds WW2 vintage as a general rule, at sea level or very low altitude for a very limited period of no more than 1 minute, though overall maximum boost pressure can be substantially increased for this period with the use of water-injection or MW-30/MW-50.

The rated altitude of the DB-603LA is 10,000 metres. The FTH is 10,500 metres. The maximum performance capabilties using MW-50 are 9500 metres (740km/h under test conditions time period unclear, ref. Joe Baugher), with maximum FTH performance at of course 10,500 metres (730km/h tested Jan 1945, ref. Focke Wulf).