The turbocharger compresses the air, and compression heats it up: at the compressor outlet, the air can exceed 150 °C. It is then less dense, meaning it contains less oxygen, and causes knocking - which the ECU corrects by retarding the ignition, in other words reducing power. The intercooler cools it before it enters the engine.

The gain is therefore less about peak power than consistency: a saturated stock intercooler lets power drop sharply on the second lap of a circuit or during the third acceleration run. Beware of the instinct to go for the biggest option: excessive volume takes longer to fill and blunts response. The right intercooler keeps temperatures under control throughout actual use.