Why is intercooling such a good thing?
Anytime you compress air, it heats up. Even at 100% adiabatic efficiency (which is impossible), the air will heat up quite a bit. The inefficiency of the compressor (turbocharger or supercharger) will heat the air up even more. As the air is heated, the density of the air drops. Engine power is a function of the amount of air, and fuel, you can get into the cylinder during the intake stroke. It is not really the volume of air but rather the mass of air that is the key. As the air is heated and the density drops, the same volume will supply less air mass to the cylinder. The key is to not only compress the air, but to cool it back down as well to achieve the maximum mass of air, and therefore maximum power. In addition to this, the hotter the inlet air, the more tendency the engine will have towards detonation and pre-ignition. These are very damaging to the engine and they rob power.
