The engine and turbo compress and heat the air charge immensely. Others have mentioned air density, but while dense air is nice, the increased temperature is the important part when it comes to high performance turbo applications. Everyone knows that overheating an engine is bad, but what actually happens when you push things too far?
If your combustion chamber grows too hot, you can suffer from pre-ignition, where your fuel-air mixture ignites sooner than it should. This results in wasted power and increased temps as the engine has to compress the now-expanding combustion charge.
What often follows pre-ignition (provided nothing has melted or blown up yet) is detonation. In normal combustion, you have a flame front that expands smoothly from the ignition spark and causes a smooth increase in pressure. It occurs quickly, but it's not an explosion. Detonation is the opposite. Pockets of fuel-air mixture in any part of the combustion chamber ignite explosively, sending out sharp shockwaves that are too fast to be absorbed by the rotating mass of the engine. If the detonations are too powerful or too frequent, they can cause catastrophic damage.
There's plenty more that can be explained on the subject and I'm sure somebody can find something to correct, but that's the gist of it. The engine is already hot enough, higher intake temps make things worse, go too far and you get abnormal combustion which results in spontaneous disassembly.
If your combustion chamber grows too hot, you can suffer from pre-ignition, where your fuel-air mixture ignites sooner than it should. This results in wasted power and increased temps as the engine has to compress the now-expanding combustion charge.
What often follows pre-ignition (provided nothing has melted or blown up yet) is detonation. In normal combustion, you have a flame front that expands smoothly from the ignition spark and causes a smooth increase in pressure. It occurs quickly, but it's not an explosion. Detonation is the opposite. Pockets of fuel-air mixture in any part of the combustion chamber ignite explosively, sending out sharp shockwaves that are too fast to be absorbed by the rotating mass of the engine. If the detonations are too powerful or too frequent, they can cause catastrophic damage.
There's plenty more that can be explained on the subject and I'm sure somebody can find something to correct, but that's the gist of it. The engine is already hot enough, higher intake temps make things worse, go too far and you get abnormal combustion which results in spontaneous disassembly.