Engine horsepower is affected by both RPM and MAP. Maximum RPM and maximum MAP produce maximum horsepower (and maximum fuel consumption). Low RPM and fairly high MAP produced the best fuel economy.
Some typical engine ratings follow:
rating max time HP RPM altitude MAP
WEP 5 min 1800 3000 sea lvl 76"
takeoff 5 min 1325 3000 sea lvl 54"
MIL 15 min 1100 3000 27,000 52"
max continuous 1000 2600 23,000 43"
(from America's Hundred Thousand, pg. 101)
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