What is the difference between a turbo-charger and a super-charger?

by | Aug 14, 2008 08:00 PM ET

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Marshall Brain

Hi, I'm Marshall Brain with today's question - What is the difference between a turbo-charger and a super-charger on a car's engine? Let's start with the similarities. Both turbo-chargers and super-chargers are called forced induction systems. They compress the air flowing into the engine. The advantage of compressing the air is that it lets the engine stuff more air into a cylinder, and more air means that more fuel can be stuffed in, too, so you get more power from each cylinder.

A turbo- or a super-charged engine produces more power overall than the same engine without the charging. The typical boost provided by either a turbo-charger or a super-charger is six to eight pounds per square inch. Since normal atmospheric pressure is 14.7 psi at sea level, you can see that you're getting about 50 percent more air into the engine, therefore you would expect to get 50 percent more power. It's not perfectly efficient, so you might get a 30 percent or 40 percent improvement instead. The key difference between a turbo-charger and a super-charger is its power supply. Something has to supply the power to run the air compressor.

In a super-charger, there's a belt that connects directly to the engine. It gets its power the same way that a water pump or an alternator does. A turbo-charger, on the other hand, gets its power from the exhaust stream. The exhaust runs through a turbine, which in turn spins the compressor. There are trade-offs in both systems. In theory, a turbo-charger is more efficient because it's using the wasted energy in the exhaust stream for its power source.

On the other hand, a turbo-charger causes some amount of backpressure in the exhaust system, and tends to provide less boost until the engine is running at higher RPMs. Super-chargers are easier to install, but they tend to me more expensive. Do you have any ideas or suggestions for this podcast? If so, please send me an email at Podcast@HowStuffWorks.com.

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