InterCooler
As air is compressed it heats up because its molecules contain the same kinetic energy except within a smaller volume. In the automotive world, hot air entering engines kills power in two ways: One, by reducing density, and thus, the quantity of the air; and two, by increasing the propensity for the air/fuel mixture to pre-ignite, causing "knock and ping" and potential engine damage. Since turbocharger compression heats our incoming air, and we want the coldest air possible to enter the engine, we turn to yet another device in the turbo system: The intercooler.
This intercooler may look like a radiator to you, and that's basically what it is. Instead of flowing hot engine coolant, the intercooler flows hot air, wicking heat to the outside atmosphere. Peering into the end of an intercooler, you can see the resemblance between its inner core and the inner core of a radiator, visible when the radiator cap is removed.
source from
http://overboost.com/story.asp?id=1048