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