Turbochargers and superchargers are great engine performance enhancers because they can pack more air into the cylinders than atmospheric pressure alone can, and as we all know, more air and a corresponding greater amount of fuel means more power. However, compressing the air also raises its temperature, and if this hot pressurized air is allowed to enter the cylinders fresh from the turbo or supercharger, it could cause engine damaging detonation.
To cool the hot compressed air, it can be routed from the turbo or supercharger outlet through an intercooler, and then to the intake manifold. An intercooler lowers the air temperature, which increases its density and oxygen content for an even greater increase in power and prevents engine knock. An intercooler enables the benefit provided by the turbo or supercharger, without the dangers and inefficiency that can result from heat. Not all older turbocharged or supercharged vehicles had intercoolers, but today they are a part of most factory turbo and supercharger setups, so the vehicle manufacturer can ensure performance with durability.
There are air-to-air and air-to-water, sometimes called air-to-liquid, intercoolers. Air-to-air intercoolers resemble radiators, function in the same way, and are typically mounted in the same area of the vehicle. However instead of engine coolant, it is hot compressed intake air that flows through the intercooler. The heat from the intake air is transferred to cooling fins and then to the ambient air that passes through the intercooler. The heat from the intake air is transferred to coolant with an air-to-liquid intercooler, with the coolant circulating between the intercooler and a heat exchanger at the front of the vehicle where the heat is then transferred to the ambient air. Air-to-air intercoolers are commonly used with turbochargers and centrifugal superchargers, while air-to-water intercoolers are positioned between the supercharger and intake manifold with Roots type and screw type superchargers 2007 Subaru Forester.