What is a Turbocharger?

Katharine Swan

As a little-know fact, a turbocharger is actually a type of supercharger. Originally, the turbocharger was called a "turbosupercharger." Obviously, the name was shortened out of convenience.

Turbochargers often work with an engine's carburetor.
Turbochargers often work with an engine's carburetor.

A turbocharger's purpose is to compress the oxygen entering a car's engine, increasing the amount of oxygen that enters and thereby increasing the power output. Unlike the belt-driven supercharger that is normally thought of when one hears the word "supercharger," the turbocharger is powered by the car's own exhaust gases. In other words, a turbocharger takes a by-product of the engine that would otherwise be useless, and uses it to increase the car's horsepower.

A turbocharger's purpose is to compress the oxygen entering a car's engine, increasing the amount of oxygen that enters and thereby increasing the power output.
A turbocharger's purpose is to compress the oxygen entering a car's engine, increasing the amount of oxygen that enters and thereby increasing the power output.

Cars without a turbocharger or supercharger are called normally aspirated. Normally aspirated cars draw air into the engine through an air filter; the air then passes through a meter, which monitors and regulates the amount of air that enters the system. The air is then delivered to the engine's combustion chambers, along with a controlled amount of fuel from the carburetor or fuel injectors.

In a turbocharged engine, however, the air is compressed so that more oxygen will fit in the combustion chamber, dramatically increasing the burning power of the engine. The turbocharger is composed of two main parts: the compressor, which compresses the air in the intake; and the turbine, which draws the exhaust gases and uses them to power the compressor. Another commonly used term in relation to turbochargers is boost, which refers to the amount of pressure the air in the intake is subjected to; in other words, the more compressed the air is, the higher the boost.

Although the increase in power is advantageous to the car -- and likely a source of enjoyment for the driver -- a turbocharger has its drawbacks. First and foremost, a turbocharged engine must have a lower compression ratio than a normally aspirated engine. For this reason, one cannot simply put a turbocharger on an engine that was intended for normal aspiration without seriously undermining the life and performance of the engine. Also, a lower compression ratio means the engine will run less efficiently at low power.

Another major drawback of a turbocharger is the phenomenon known as turbo lag. Because the turbocharger runs on exhaust gases, the turbine requires a build-up of exhaust before it can power the compressor; this means that the engine must pick up speed before the turbocharger can kick in. Additionally, the inlet air grows hotter as it is compressed, reducing its density, and thereby its efficiency in the combustion chamber; a radiator-like device called an intercooler is often used to counter this effect in turbocharged engines.

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Discussion Comments


@titans62 - I'm pretty sure a turbocharger rarely if ever can increase the fuel economy of a car.

I know a guy who decided to buy a turbocharger and install it on his car. He swears that it increases the fuel efficiency, but I can't imagine it. In theory, it could be true because with the increased air compression, you would be more likely to combust all of the fuel.

The problem is that turbochargers actually end up using extra fuel for other purposes. The article mentions an intercooler, which are notorious for getting small holes and releasing air and significantly lowering fuel economy.

Besides that, just the fact that you have a turbocharger and have the ability to drive faster means you will probably accelerate faster than you would in a normal car, thereby using more fuel that way.


@cardsfan27 - I'm completely with you about what I consider to be the worthlessness of a turbocharger. As far as I am concerned, it is just something that car makers are putting on sportier cars to try to make them more appealing to buyers.

I also have a friend who keeps wanting a car with a turbocharger in it. The problem is that we live in a city of about half a million people and horrible traffic. Even if he had a car with a turbocharger, he'd never have the opportunity to use it except on the interstate. You're lucky to ever be driving over 30 through the town itself.

As far as fuel consumption goes, I'd also be interested to hear about that. I can't imagine a turbo making the mileage any better.


@cardsfan27 - Good questions. As far as the exhaust goes, that air never actually gets circulated back into the engine. It is just used to turn a turbine in the turbocharger that helps to compress the air. After the exhaust goes through, it gets released. You're right though, if that air went back in the engine, there wouldn't be enough oxygen to power the car.

That leads into the difference between the two chargers. Basically, a turbocharger is exactly what the article describes. It is a special attachment for the engine that recirculates exhaust to compress the air.

A supercharger, on the other hand, is attached by a belt to the engine, and the power from that belt is what generates the compression of the air.


So, what exactly is the difference between a turbocharger and a supercharger? One of my friends keeps talking about getting a car with a turbocharger in it, and I can't really see the point.

How does fuel consumption differ when using a turbo? Does the car actually put more fuel into the system because there is more room in the cylinder, or does all the extra space just get filled up with highly compressed air?

Also, how does the rest of the exhaust system work if all the air gets funneled back into the turbocharger? Does the same air get cycled through over and over or does it just take one or two trips through the turbocharger before it is expelled? I'm just wondering because even though catalytic converters can pull out a lot of the impurities in the spent air, there is still carbon monoxide and other gases mixed in with the exhaust.

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