Ideally Louis, you want the Intake Runner Tempature to be as close to ambient (or even below ambient) as you can get it.....to stave off detonation as long as possible.
Air to Air intercoolers BLOCK airflow into the front of your car,....or at least a properly sized one would......Air to water coolers use up the reservoir due to the conductive heat dissapation they employ....they work good, they are just more complicated.
Water Injection....turned on at a temp such as 150* charge air temp, would be best.....but knowing inlet temps can exceed 150 while NOT on boost, idling, cruising ect....its best to activate the system by pressure....and like I said....with a Adjustable Hobbs Pressure switch you can make the system come on at 1 psi if you wanted.
