Originally Posted by Stu @ M Developments
Sorry, whilst that is an interesting theory, it is largely incorrect.
The temperature of the air PRIOR to the inlet valve closing dictates quite substantially the actual amount of oxygen present in the cylinder and thus affects both the Peak Cylinder Pressure & thus the burn time / advance requirement. This is of course one of the main reasons we fit intercoolers.
That's a bit too rule of thumb...
Some more detail needed here..
400 c is the threshold where auto-ignitive species will develop, whether your inlet air charge is 20 c or 40 c. The colder the air charge, the faster it will rise in temperature, fuel will slow this rise as it soaks its fair share from cylinder wall heat transfer. The air and fuel mixture together will rise in relation to cylinder wall temperatures, and compression from the piston. A rise in temps untill equlibrium is reached that is.
Intercoolers aren't solely used to prevent knock, they were fitted to remove the heat added by the process of compression whilst maintaining the pressure differential between the cylinder vacuum and the pressurised air supplied by the compressor. All this means is that air mass is maximised at the set boost pressure.