Originally posted by rrmike
Cool air is also important for another reason. To prevent detonation.
The few degrees of difference in intake temperature has no effect on detonation/preignition/dieseling. If it did, you'd have to reset your timing every summer. Spark plug type, ignition timing, octane, & combustion chamber geometry have MUCH more effect on detonation than a couple of degrees in the intake. The intercooler has nothing to do with it.
Originally posted by rrmike
Once the air has passed through the turbo or blower then cooling it for the purpose of making it more dense is seemingly pointless. The charge of air in the intercooler is already set before the air is cooled. Making it more dense will not create more O2 molecules.
But making the air charge cooler/denser also reduces the head pressure at the turbo/SC outlet, which allows more flow in the same size pipe, so there's more free space in the engine compartment. And it has to be done after the compression because compression causes some of the heat & temperature that you're trying to get rid of.
The air charge isn't SET by any one part of the intake system - it depends on MANY factors, and reducing the pressure at any point will have a significant effect on total flow.