Superchargers and turbochargers both serve to increase an engine’s power by forcing a larger air-fuel mixture into the engine than it would normally get, but they go about it in different ways.
What’s a Supercharger?
A supercharger is a rotating air pump that’s driven by the engine itself via a belt or chain run off the engine’s crankshaft.
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Although it saps some power to make it turn, a supercharger usually spins at a speed directly proportional to engine speed, so the added pressure it provides tends to be quite consistent, resulting in quick, relatively linear power delivery. This type of power delivery is a supercharger’s primary benefit.
What’s a Turbocharger?
By contrast, a turbocharger consists of two turbine wheels — somewhat like fan blades — and is driven by the pressure and heat of the engine’s exhaust.
The two turbine wheels are fixed to opposite ends of the same shaft, and each turbine wheel is carried in its own chamber. One turbine wheel is spun by the pressure and heat of the exhaust (sometimes called the hot side), and it spins the other turbine wheel that pressurizes the air-fuel mixture (the cold side), forcing more of it into the engine’s cylinders.
However, because it takes time to spin the turbine wheels fast enough to build up this added pressure, the power increase it provides sometimes takes a bit to arrive after the throttle is pressed. This is called turbo lag. On the contrary, it can sometimes come on in a sudden rush, which might make the vehicle difficult to control.
Because it’s driven by the exhaust that’s exiting the engine anyway, a turbocharger bleeds off less power than a supercharger — a benefit — but it also often delivers delayed, nonlinear power — a demerit in some cases.
However, some of the turbocharger’s inherent drawbacks have been at least partially addressed. Turbo lag and the occasional power rush have been reduced by new designs or by using two turbos — one or both being smaller — in place of one large one since the smaller ones spin up to speed faster. These twin turbos are particularly popular in V-6 and V-8 engines, as one turbocharger can be fitted to each of the two banks of cylinders. These advances have made turbochargers far more popular in recent years.
Why Superchargers and Turbochargers Are More Powerful Than a Traditional Engine
Engines without a supercharger or turbocharger are referred to as naturally aspirated. When one of the cylinder’s pistons drops down on its intake stroke, a vacuum is formed above it. That vacuum is filled by the air-fuel mixture rushing in under normal atmospheric pressure of about 14.7 pounds per square inch at sea level.
When a supercharger or turbocharger kicks in, it forces in more of an air-fuel mixture than would otherwise be drawn in, creating a bigger reaction, which makes for more power. In both cases, the amount of added pressure provided is known as boost.
If you hear an expression that a supercharger or turbocharger produces 10 pounds of boost, that means it forces the air-fuel mixture into the cylinder at 10 pounds more pressure than the 14.7 pounds of atmospheric pressure alone.
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