The turbocharger compresses 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 it causes knock - which the ECU corrects by retarding the ignition, resulting in lost power. The intercooler cools it before it enters the engine.

The gain is therefore less about peak performance than consistency: a saturated stock intercooler lets power collapse on the second lap of a circuit or during the third acceleration. Beware of the “bigger is better” reflex: excessive volume takes longer to fill and dulls response. The right intercooler keeps temperatures under control throughout real-world use.