A turbocharger borrows the energy in the exhaust to push more air into the engine. Use the buttons to look inside it and follow the air and the exhaust around the loop, from the filter to the spare heat that is normally wasted.
A turbocharger is a device that uses the energy in an engine's exhaust to force more air into the engine. More air means more fuel can be burned, and burning more fuel means more power from the same engine. It spins on the very gas that would otherwise simply be let out of the tailpipe.
The trick is a shared shaft. Hot exhaust leaving the engine spins a turbine on one end of the shaft, and the compressor on the other end turns with it. The compressor squeezes fresh air, an intercooler cools that squeezed air back down, and the engine gulps the denser charge. In a car engine, the turbo often whistles as it spools up.
From the outside a turbocharger is just a metal snail bolted to the exhaust. Its two wheels, the shaft that links them and the wastegate that controls the boost are all hidden inside, so opening it up shows why the exhaust and the intake are really two ends of the same machine.
One idea holds it together: energy that would be thrown away as hot exhaust is captured, spun back into the intake, and turned into extra power. The wastegate is simply the safety valve that stops the loop from running away with itself.
Everything starts with the intake. Air is drawn in through the air filter, which traps dust before it can reach the compressor. Clean incoming air is the raw material the whole turbocharger works on.
The compressor is the first wheel on the shared shaft. As it spins it flings air outward and packs it into a smaller space, raising the pressure. Squeezing air also heats it, so what leaves the compressor is a hot, dense charge — denser than the air that came in, which is the whole point.
Hot air is less dense than cool air, so the charge is passed through an intercooler before it reaches the engine. The intercooler pulls heat out of the air; cooler air is denser, so more of it fits into the cylinder, and the engine is less likely to knock.
After the intercooler the pressurised air passes a throttle, which controls how much of it is allowed through. The throttle is what your right foot ultimately moves, so the driver decides how much of the available boost actually reaches the engine.
Inside the engine the dense air is mixed with fuel and burned. More air and fuel in the same cylinder means a bigger, stronger power stroke — the extra air the turbo worked so hard to pack in is what makes the extra power.
Burning produces hot exhaust gas, and it is still full of energy. That gas is aimed at the turbine, the second wheel on the shaft, and spins it as it rushes past. The turbine then turns the compressor through the connecting shaft, so the engine's leftover heat drives its own air supply.
Left alone, the turbo would keep spinning faster and faster and the pressure would climb too high. The wastegate is a bypass valve: as boost builds it opens a path that lets some exhaust skip the turbine, so the turbo slows and the pressure is held at a safe level. The spent gas finally leaves through the exhaust outlet.
From the exhaust. Hot gas leaving the engine spins a turbine, and the turbine turns the compressor through a shaft between them. Nothing is driven off the engine's belt, so the boost is close to free energy recovered from the exhaust.
It squeezes the incoming air. More air in the same cylinder means more fuel can be burned, and burning more fuel makes more power from the same engine.
Compressing air heats it, and hot air is less dense. The intercooler cools the air back down before it reaches the engine, so more of it fits in and the charge is less likely to knock.
It is a bypass valve that lets some exhaust skip the turbine. As boost builds, the wastegate opens to hold the pressure at a safe level instead of letting the turbo spin ever faster.
The turbine needs moving exhaust gas to spin up, so when you press the accelerator there is a short delay before the boost arrives. That delay is turbo lag; it is shorter when the engine is already revving and the exhaust is flowing.
Because the turbo runs on exhaust gas, pressing the accelerator first has to build up exhaust flow to spin the turbine and compressor. That short delay before boost arrives is turbo lag. A smaller, lighter turbo, a twin-scroll housing, an electric turbo, or a belt-driven supercharger helping out can all shorten the wait.
Both squeeze the air going into the engine so more fuel can be burned and more power made. A turbocharger is driven by the exhaust gas, so boost builds with a slight delay but reuses energy that would otherwise be wasted. A supercharger is driven directly by the engine's belt, so it responds immediately but takes power from the engine to run.
It uses movable guide vanes in the turbine housing to change the angle and speed at which the exhaust hits the turbine wheel. At low engine speed the vanes narrow the passage to speed up the exhaust and cut lag, and at high speed they open up to prevent over-boosting.