Been watching some YouTube videos about these engines and the amount of boost they ran . I figure all of you know , the more boost you run , potentially , the more hp , all things being equal . Untill something comes apart . The main comparison was between the Merlin engine in the P51 Mustangs , and various British planes . And the engines used in the BF-109 . I guess the bottom ends were mostly strong enough not to be the limiting factor . Apparently the biggest limiting factor was detonation . Apparently , the generally Allies had higher octane fuel . This allowed them to run higher boost , resulting in higher HP . The supercharger design played a part too . And they could be optimized for a specific altitude range . Some engines used 2 speed superchargers , also . Then I watched a video about water / methanol injection . Apparently , this was used in some models of German engines / planes . The net result was the ability to run higher boost , before the onset of detonation . Can not remember if any Allied planes use WM injection ? On a slightly different subject , I read some early jets used water injection , on take off , I think . I found all this interesting .