If you have ever noticed in this game, engine off on the runway there is no real "air" in this game. Manifold pressure is as low as the gauge can go (when in real life at sea level its around 29.9 inches and -1 per 1k of alt) and the engine temp is 0*C which is freezing. My request is much like wind to have some air to this game with temperature and pressure. Next we could have some high and low pressure zones which would impact manifold pressure and thus change the way the gauge is referenced. Currently and quite unrealistically its a "this % of power is used with this offset and this max %". Instead it should also tell you things about the world you're actually flying in! Also humidity and temperature can play apart in how much power a certain engine makes. While some may say it doesn't change game play I think it does two things:
1: Makes the game more realistic and immersive.
2: Makes the pilot understand the gauge and how its used more than just some "engine power thingy" as it can also be used to check alt.
3: Allows weather effects such as rain do something (raise humidity).