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Turbocharging or supercharging?

Turbochargers and superchargers are two methods for achieving forced induction. In other words, pressurising air before it enters the engine’s combustion chambers (cylinders) in order to provide a greater mass of oxygen.
The whole point of this is to increase the power and torque outputs of an engine, albeit artificially. In fact, adding forced induction to an engine gives power outputs normally associated with a bigger cubic capacity.

How do they work?

Both utilise a spinning impeller, or screws in the case of some superchargers, to compress air before ejecting it into the induction system. On the turbocharger this impeller is linked via a shaft to a sealed turbine mounted onto the engine’s exhaust manifold. The exhaust gases escaping from the engine are thus used to spin this turbine, which in turn spins the shaft linked to the impeller. It is almost like a partial recycling of the spent exhaust gases to help boost the engine’s performance.

On the supercharger the impeller is usually spun by a chain, shaft or gear and in some cases a belt and pulley linked to the engine’s crankshaft. In some installations the supercharger remains permanently connected, an example would be the earlier BMW MINI Cooper S R53, in other older installations they would be governed by a small clutch unit which the driver could engage or disengage using a small lever or electrical switch control.
So a turbocharger is actually a type of supercharger, a turbo-supercharger. But we have come to refer to them as turbochargers (or “turbo” for short) and now refer to mechanically driven systems as superchargers.

Which is better?

The turbocharger requires an intricate and somewhat complex installation onto the exhaust system, in order to provide exhaust gases to spin the turbine, but also needs a system of tubing to the impeller and then from the impeller to the engine’s induction manifold. This takes up a certain amount of space but also contributes to an increase in engine bay temperatures. The advantages are that the turbo recycles part of the waste exhaust gases to give a power increase and doesn’t sap engine efficiency by being mechanically linked to it.

Unfortunately, it takes a short while for the turbine to spin up to speed and provide the extra power, which results in a short delay referred to as “turbo lag”. This is not a problem for the supercharger as it spins at a rate that is constantly linked to the engine’s linear increase in revs. This means that the supercharger can boost the engine at low revs, contrary to the turbo which will boost it at a slightly higher rev range. However, linking a unit like this to an engine will make the engine work harder as it has to drive the supercharger and will therefore make it less fuel efficient.

Can I have both?

Yes, in some engines, the makers have installed a supercharger for boosting at low revs and a turbocharger that takes over from the supercharger unit higher up in the rev range, an epic example of this is visible in the Lancia 038 Delta S4 rally car.

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