The big deal with detonation is just that: it is a
detonation of the air-fuel mixture. In ordinary combustion, the mixture
burns (albeit burning quite fast), but when yo uexceed certain pressures, you end up with an explosion in the engine. Not good, to say the least.
The prime contributors are compression ratio, and boost pressure. What we are really interested in is the pressure within the combustion chamber, but that is nearly impossible to measure on a running engine. So, knowing the boost pressure (which gives us the starting pressure) and the ratio by which it is compressed by the piston, we end up with an approximation of the final pressure.
But, things like combustion chamber design, spark plug design, and materials used can greatly affect things. For one, aluminum heads resist detonation better than iron heads. As well, the shape of the chamber and the spark plug can play a part, since sharp edges serve as starting points for detonation. Of course, if you totally rounded-off your spark plug, spark power would suffer. The key is in achieving the correct balance: you want to encourage fast burning, without crossing into explosions.
Inlet air temp does also play a role, but its effect on power is more important than its effect on detonation. The idea of forced induction is to put more oxygen molecules into the clyinder. Hot air is less dense than cold air, so pumping a lot of hot air into the cylinder is equivalent to pumping only a little cold air into it. Of course, if we add an intercooler, then we can pump a lot of cold air in, and have the best situation
Joe
