In real life, the effect of too much manifold pressure on any supercharged engine, be it a Porsche 911 or a P-51, is too exceed the ability of the fuel being used to work without detonation.
Running on methanol an internal combustion engine can take as much boost as it can mechanically stand before cylinder pressure pulls it apart, but regular petrol or gasoline has an octane rating and each of those ratings, 91 octane for instance, can only stand so much heat and pressure before instead of waiting for the timed ignition from a spark plug, it ignites spontaneously. This detonation can begin in more than one point in the engines combustion chamber and it produces super-sonic wave-fronts that collide with each other and produce enough force and energy to not only be heard outside the thick castings of the engine, the forces will blow engine parts to pieces, splitting cylinders and breaking pistons, combustion chambers and spark plugs.
So at high altitude when the air gets thin and air pressure and the amount of oxygen goes down, you either have to change the amount of fuel to match the amount of oxygen, or you have to cram more air into the engine to match the existing amount of fuel, or both! There is a specific fuel-air ratio that will give not only good power, but also good economy and it even cools the intake charge and engine a bit to prevent detonation. Too rich a mixture, meaning too much fuel for the available air, and the fuel that is not burned will get into the engine oil, make the engine run too cool and it will foul spark plugs and get in the way of clean burning, black soot comes out of the exhaust pipes!
If the mixture of the fuel is perfect for combustion or lean, where there is only enough fuel to perfectly match the number of oxygen molecules in the burning reaction, or if there is not enough fuel, then the engine will burn hot and either melt the pistons, burn the exhaust valve, or be destroyed by detonation.
The hotter the engine cylinder head, the cooler or less dense the intake charge has to be to prevent detonation. Supercharging intercoolers run the intake charge through radiators to cool it, because compressing air in a supercharger heats it up!
So here is the big trade off: The air is thin up high, so we compress the air to get the amount going in the engine back close to what it is closer to sea level, but when we compress it in the supercharger it heats up, and hot air is thinner and causes detonation, so we have to add more weight and complexity to the aircraft to install an intercooler and hopefully the added weight does not destroy the benefits of the intended use of the machine we are flying. We also have to install either manual or automatic devices to alter the fuel mixture to keep it correct for all the different air densities at all the different pressures and temperatures the outside air is to begin with.
Now you see why it is called COMPLICATED engine management. The ignition timing of the engine ideally even is altered to match different octanes of fuel and different temperatures.
This is why people with no mechanical aptitude or understanding simply can not get the most out of older internal combustion engines, especially high-performance ones.
Now in 2012, all your automobiles and other vehicles with an ICE have a computer which controls spark timing, fuel mixture and even valve timing and shifting of the transmission and supercharger wastegates. But in 1940 the only computer available to do all this was either by inventing complicated mechanical mechanisms such as the Diamler-Benz mechanical fuel injection, or the computer was simply in your head, which used your hands to flick switches and twirl knobs to keep all the above parameters in the correct range.....
S!
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