Academy · Car Engines · Lesson 7/11
Forced induction
Turbochargers and superchargers: stuffing in more air. ~6 min
Lesson 6 ended on a cliff: past a certain speed an engine simply cannot suck enough air. Forced induction is the blunt, glorious answer — stop sucking, start pumping. Compress the air before it reaches the cylinders and every gulp carries more oxygen, every bang burns more fuel, and a small engine hits like a big one. It is the single biggest power multiplier in engine history.
Why dense air is power
A cylinder's volume is fixed — but the mass of air inside it is not. Squeeze the intake air to 1.5 bar (half again atmospheric) and each intake stroke swallows roughly 50% more oxygen, so the engine can burn ~50% more fuel: near enough 50% more power from the same engine. That is why a modern turbocharged 1.5 fills the role a 2.5 once did, and why F1 gets 1000 horsepower from 1.6 litres.
The catch: compressing air heats it, and hot air is both less dense (undoing part of the gain) and prone to knock (next lesson). So nearly every boosted engine feeds the compressed air through an intercooler — a radiator for air — before the cylinders. Cool it back down, keep the density, keep the safety margin.
Turbocharger: powered by rubbish
The exhaust leaving an engine still carries around a third of the fuel's energy as heat and velocity — normally wasted. A turbocharger puts a turbine in that stream: exhaust spins the turbine, the turbine spins a compressor on the same shaft at up to 200,000 rpm, and the compressor pumps the intake. Boost, powered by garbage — which is why turbos are the efficiency choice, and why nearly every new engine wears one.
The flaw is famous: turbo lag. The turbine needs exhaust flow to spool up, but big exhaust flow needs boost — a chicken-and-egg pause between pressing the pedal and the shove arriving. Modern fixes: smaller, quicker twin-scroll turbos, two turbos of different sizes, or — the F1 solution — an electric motor on the turbo shaft to spin it up instantly.
Supercharger: powered by the crank
The older solution drives the compressor directly from the crankshaft by belt or gears: the supercharger. No lag whatsoever — boost arrives exactly with the revs — and a snarling character all its own. The price is honesty: driving the compressor can steal tens of horsepower from the crank, power the turbo would have scavenged from the exhaust for free. Superchargers ruled the pre-war Grand Prix era and still suit big muscle-car engines; turbos won the efficiency age.