Because now the turbo speeds up to a hundred thousand of revolutions, density goes up in the air is compressed in the process, this will cause the air temperature increases, thus affecting the volumetric efficiency of the engine. If you want to further improve the volumetric efficiency and lower air inlet temperatures. Data show that, under the same conditions of air-fuel ratio, pressurized air temperature of 10 c, the engine power can improve 3%~5%.
Without cooling the pressurized air into the combustion chamber, will affect the volumetric efficiency of the engine, but also easily lead to engine temperature is too high, causing detonation failure, and increase of engine exhaust gas NOx content of air pollution. Increasing role of cooler is to cool the intake air temperature, rather than upstairs said turbocharger temperatures.