Here is the BMW 801D-2 data I used. My interpretation of the notation might be off. Assistance would be appreciated...
On another note, I am using uninstalled engine performance and bookkeeping installation effects as drag.
Title of the graph says that it denotes power available to the prop + power to turn the cooling fan ( 'Wellen- + Luefterleistung').
The thick lines are for 'Mit Stau' condition, ie 'with ram effect' - that means engine is not just installed, but the aircraft is moving at a very high horizontal speed. Another note says 'Stauausneutzung 70%', ie. engine uses 70% of ram effect out of 100% that is theoretically possible.
Thin lines are for the case without ram effect - 'Ohne Stau'. For the fully rated engine, and without overboost (= 2700 rpm, 1.42 ata), the best value in 2nd gear, total power plotted at ~18500 ft as 1560 PS. The fan required, at least on the BMW 801S, some 70 PS at 2700 rpm, so the actual power available to the prop is a bit under 1500 PS at that altitude. A bit more generous than the values from the manual, but we can probably live with it.
Graph denoted as 'mit Alkoholzusatz' - basically if MW50 is used - gives far better power values, however the MW 50 was not used operationally on the BMW 801.
Please note that German equivalent of 'military power' for the BMW 801 is the case of 2700 and 1.42 ata. The 'dry' overboost, as it was the case with allowing up to 1.65 ata operation on the fully-rated engine would've been called 'WER' on US terminology; water-alcohol use on US engine was called also WER, and sometimes 'WER wet'.
The line for the DB 605A on your graph is for the restricted engine - 2600 rpm, 1.30 ata max - that was good for 1250 PS at 5.7 km (1300 PS at S/L). For the fully rated engine, making 2800 rpm and 1.42 ata max, usually dated from October 1943 on, power was 1350 PS at 5.7 km, and 1475 PS at S/L.
Fellow members and yours truly have posted a number of graphs
in this thread, FWIW.