“An intercooler is a heat exchanger used to cool a gas after compression.Most commonly used with turbocharged engines, an intercooler is used to counteract the heat of compression and heat soak in the pressurised intake air. By reducing the temperature of the intake air, the air becomes denser (allowing more fuel to be injected, resulting in increased power) and less likely to suffer from pre-ignition or knocking. Additional cooling can be provided by externally spraying a fine mist onto the intercooler surface, or even into the intake air itself, to further reduce intake charge temperature through evaporative cooling.
Intercoolers can vary dramatically in size, shape and design, depending on the performance and space requirements of the system. Many passenger cars use either front-mounted intercoolers located in the front bumper or grill opening, or top-mounted intercoolers located above the engine. An intercooling system can use an air-to-air design, an air-to-liquid design, or a combination of both.” (refer to wikipedia)