High-altitude developments
Limitations of A series
The BMW 139 (and the 801 that followed) had originally been designed as a high-power replacement for earlier engines like the BMW 132 that were used primarily on low-altitude cargo aircraft and bombers. As a result, the designers had not invested much effort in producing high performance superchargers for it.
Even before the Fw 190 A was put into service, its high-altitude performance was seen to be deficient. In contrast, the Daimler-Benz DB 601 engines used on the Bf 109 featured an advanced fluid-coupled, single stage, variable speed supercharger that provided excellent boost across a wide range of altitudes. The 190's short wings also presented a problem at higher altitudes, where they were highly loaded. As a result, the 190 could not compete with the 109 at altitudes above 20,000 ft (6,100 m), which is one reason that the 109 remained in production until the end of the war. This was not a serious concern at the time of introduction, as most combat was taking place at medium altitudes, where the 190 had ample performance.
However, as the air war reached higher altitudes with the widespread introduction of turbocharged US bombers, the need for improved performance became pressing. As a result, GM-1 Nitrous oxide boost was introduced to provide more power at altitude, but this was complex and gave boosted performance for only a short period of time.