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How Does a Supercharger Work?

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Although there are different types of superchargers, all serve to force more air into an engine than it could draw in on its own, thus allowing the engine to produce more power. The same could be said for a turbocharger; see them compared.

Related: What’s the Difference Between a Supercharger and a Turbocharger?

The three most common types of superchargers are the Roots (named after its inventor, Francis Roots), twin-screw and centrifugal. All are driven by the engine itself — typically through a belt off the crankshaft — though the centrifugal type could also be driven by an electric motor. However, that would likely take a more powerful motor, which in turn would require a rather robust battery to power it.

By contrast, a turbocharger is driven by engine exhaust gases, not the engine’s rotating crankshaft.

How Superchargers Work

Each supercharger type works somewhat differently. The Roots and twin-screw both can have two parallel, rotating internal shafts with lobes on them that mesh in such a way as to move air through the supercharger and into the engine. In the case of the Roots, it simply pumps more air through than the engine could otherwise draw in; the twin-screw, however, compresses the air between the two shafts as it flows from one end to the other and then forces the air into the engine.

A centrifugal supercharger works much like a turbocharger except an impeller fan that spins fast enough to pump in lots of air is driven by the engine’s crankshaft (or an electric motor) rather than the engine’s exhaust gases.

In modern engines with fuel injection, the supercharger just pumps air, which gets fuel added to it after the fact. Since fuel is added in a proportionate amount, more air means more fuel can be added, and that larger quantity of air-fuel mixture can create more power.

In all cases, engine-driven superchargers require some engine power to turn them, and that means they bleed off some power that’d otherwise go to the wheels. This is the reason for driving a centrifugal supercharger with an electric motor — though, again, that would require a big motor, a big battery to power it (not necessarily for long) and engine power to turn the alternator to recharge the battery. The advantage is the engine power wouldn’t necessarily be required at the same time you were trying to accelerate; it could wait until you were going to decelerate, when you wouldn’t need power anyway.

One note: When added power isn’t required — which on a regular car is most of the time — a bypass valve is typically activated so air is drawn in normally rather than being forced in under pressure. This greatly reduces the amount of power used to turn the supercharger.

When more power is called for — a stomp on the gas pedal, in other words — the bypass valve closes and the supercharger goes to work. Typically, this takes place inside the supercharger body, which is usually about the size of two side-by-side bread loaves in the case of the Roots and twin-screw and more cantaloupe-sized for a centrifugal.

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Which Supercharger Is Best?

Which is best largely depends on how much space you have and where you want to add power.

The Roots and twin-screw superchargers generally require more space and power to turn, and provide a boost in power over a wide range of engine speeds. By contrast, a centrifugal supercharger is usually smaller and takes less power to turn; it mostly increases power at the higher end of the engine-speed range.

An exception is if the centrifugal supercharger is driven by an electric motor. In that case, the electric motor can turn the supercharger at any speed desired, thus providing a boost in power on demand.

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