The old fighter planes had an entirely different set of problems to work with. The P 51 was liquid cooled where as most of the others were air cooled. The air cooled engines had cowl flaps to maintain cylinder heat temps in the "green" to prevent detonation (hot) or excessive fuel consumption (cold) These flaps were open for take off and landing and were mostly fully closed when at high altitude cruise. Opening the cowl vents too early or going full open at too high an altitude could cause rapid cooling and a bunch of warped heads, jugs etc. The P 51 radiator cooling air could be regulated also, but usually was not required. The unique way the aircraft was flown for the long range, high altitude bomber escort missions was developed by Charles Lindberg. Upon reaching cruise altitude and airspeed, they would lean the engine back until it quit, then slowly increased enrichment until it fired and then they set the throttle and mixture there. As fuel burned off, they would slowly climb, maintaing air speed and throttle/ mixture settings. Lindberg had to prove to all the old time aircraft engine mechanics that this procedure and super lean fuel mixtures did not damage the engines. His procedure increased the range of the aircraft by about 50% and were the only aircraft that could escort the bombers to Berlin and beyond.