If it is a radiator that you are looking at, this is probably the intercooler. Follow the attached hoses, probably quite large bore, one will go to the turbo, the other to the engine intake.
When the turbo pressurises the intake air, the air gets warmer. Warmer air is less dense and therefore will burn less fuel, so less power than denser air. (This is why a normally aspirated engine, especially petrol, seems more powerful on cold damp days as the air is more dense.) So although you are pushing more air in than without the turbo, some possible gains are lost due the heating of the air. The pressurised air is therefore fed through the intercooler. This uses outside air to cool the pressurised air, making it more dense, so adding to the gain. More power. The intercooler is just a radiator with air inside and outside.
Hopefully this is clear, if not tell me what needs clarification.
