A turbocharger is actually a type of supercharger. Originally, the turbocharger was called a "turbosupercharger." Obviously, the name was shortened out of convenience.
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.
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
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.