Mustang,
None of the test of the BMW801D series list "micro-cracks" in the cylinder head as an issue. Where did you get that information from?
The first test in 1941 had an issue with the zinc lining of the tank peeling off. Other than that, Alkohol-Einspritzung was authorized but not adopted because it simply did not deliver the power gains that C3-Einspritzung.
C3-Einspritzung is were fuel was sprayed into the supercharger intake. Its major drawback was thin air made the mixture too rich and the power gains dropped substantially. An altitude restriction of 1Km or below was placed on the system and could be used for two ten minute intervals. The system was fitted to ground attack and bomber variants.
Erhöhte Notleistung in the fighters was just a simple manifold pressure increase and came about because of knock limited performance of the C3 fuel was raised. It did not develop as much power as the other boost systems but did not require heavy additional equipment such as an auxiliary tank. It could only be used once for 10 minutes.
GM-1 was lighter than a turbocharger and offered good power gains at altitude. Its drawback was the altitude restriction and the system was vulnerable to intake icing.
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