Otto Explains — Turbo vs Supercharger
Turbocharger vs Supercharger: What’s the Difference?
Short Answer
Both push extra air into the engine so it can burn more fuel and make more power from the same engine size. The difference is what drives them. A turbocharger is spun by the engine's exhaust gas, while a supercharger is driven mechanically by the engine, usually by a belt from the crankshaft. That is why a supercharger can give boost from low engine speed, while a turbocharger can show a short delay, called turbo lag, before its boost builds.
Why do turbochargers and superchargers add power?
An engine's power depends on how much air and fuel it can get into its cylinders. Both devices compress the air going into the engine, so each cylinder takes in more air and can burn more fuel, which gives more power from the same engine size. Compressing air also heats it, so many engines have an intercooler (charge-air cooler) that cools the compressed air, making it denser and more resistant to knock.
How does a turbocharger work?
A turbocharger uses energy in the exhaust gas. The hot exhaust spins a turbine, which turns a compressor on the intake side through a shared shaft. The turbine creates some backpressure in the exhaust, and boost is usually controlled by a wastegate, a valve that lets some exhaust bypass the turbine. Because the turbine needs enough exhaust flow to spin up, a turbocharged engine can respond with a short delay when you accelerate from low engine speed. This turbo lag is normal: larger turbochargers tend to make it more noticeable at low speed, and the engine's calibration is designed to reduce it.
How does a supercharger work?
A supercharger is driven by the engine itself, usually by a belt or sometimes by gears from the crankshaft; some are driven by an electric motor instead. Because it doesn't wait for exhaust flow, a mechanically driven supercharger can provide boost from low engine speed. The trade-off is that a belt-driven supercharger turns whenever the engine turns, unless a clutch disengages it, and that costs some efficiency through parasitic losses. Some designs therefore use a clutch to engage it only when boost is needed.
Can an engine have both?
Yes. Volvo's two-litre T6 Drive-E petrol engine, for example, uses a supercharger to fill in torque at low revs and a turbocharger that takes over as the airflow builds. Combining them uses the supercharger's quick response at low engine speed and the turbocharger's use of exhaust energy higher up.
What does this mean for owners?
A turbocharger depends on engine oil for lubrication, and manufacturers give their own advice for looking after it. Kia, for example, advises not revving the engine straight after a cold start and letting it idle for about 1 minute after high-speed or heavy-load driving before switching off, because switching off immediately can damage the engine or turbocharger. Follow the advice in your own manual. A turbocharged car that suddenly feels weaker than usual has several possible causes, covered in why a car loses power. Fitting a larger turbocharger is one of the major changes that tuners group under higher tuning stages. At AutoTronix, AutoTronix Garage handles engine diagnosis and repair, and AutoTronix PERFORMANCE handles performance vehicles and upgrades, subject to the vehicle's compatibility and a technical assessment.
Common Questions
- Is a turbocharger or a supercharger better? Neither is better in every way. A supercharger gives boost from low engine speed but costs some efficiency because the engine drives it, while a turbocharger uses exhaust energy but can lag before its boost builds. Manufacturers choose one, or both, to suit the engine.
- Is turbo lag a fault? No. A short delay before boost builds when you accelerate from low engine speed is a normal characteristic of turbocharged engines. A sudden or new loss of power is different and is worth having diagnosed.
- What does an intercooler do? It cools the air after the turbocharger or supercharger has compressed it. Cooler air is denser, so more of it fits into the cylinders, and it is more resistant to knock.
- Why do some manuals say to let a turbo engine idle before switching off? To let the turbocharger cool. After high-speed or heavy-load driving, Kia advises idling for about 1 minute before switching off, and warns that switching off immediately after heavy load can damage the engine or turbocharger. Other manufacturers' advice may differ, so check your manual.