A supercharger is any piece of equipment that compresses the air being delivered to an engine, allowing the combustion chamber to be overfilled without enlarging the space. The higher concentration of oxygen provided by this equipment is matched with a larger amount of fuel from the fuel injectors. By this definition, a turbocharger is actually of the supercharger family, although it is often thought of as a completely different kind of device.
A supercharger comes in two different variations: positive displacement, and dynamic. A positive displacement supercharger pushes air into the engine at a constant speed, while a dynamic one uses velocity to manipulate the pressure in the air. In either case, oxygen is compressed as it is delivered to the engine, allowing more power to be gained from every explosion in the combustion chambers. In contrast, cars that do not have this device draw air in using its natural flow, monitoring and regulating the amount via sensors and valves; these cars are called naturally aspirated.
These devices are also categorized according to how they is powered. Some superchargers, known as turbochargers, use exhaust gases to power the compressor. The exhaust gases are converted to power in a device called a turbine. Others are mechanically powered by the engine, typically via a drive belt, but also sometimes via a chain or gear. This type is what is normally called a supercharger, or a "blower," even though all systems that compress the air going into an engine are technically superchargers, regardless of how they are powered.
A mechanically powered supercharger has some of the same drawbacks as a turbocharger, such as causing shortened engine life, particularly if installed incorrectly. Because of the extreme increase in power, supercharged engines require a lower compression ratio to avoid damage to the engine. For this reason, a supercharger should not be installed on a normally aspirated car without first making the required changes to the engine. Also, when installing the device, the owner of the car should thoroughly research the effects the alteration will have on the drivetrain warranty, if the car is still under warranty.
However, a mechanically powered supercharger is superior to a turbocharger in several ways. First of all, because the power is derived directly from the engine itself, there is no delay before the device starts compressing the intake air. A turbocharger, on the other hand, must wait for the exhaust gases to build up before there is enough to power the compressor. Also, a mechanically powered supercharger suffers less of the heat-related problems of a turbocharger, allowing it to run at greater efficiency. It can even increase a car's gas mileage when used in a small car with a small engine.
Three types are commonly used in cars. The root type and twin-screw type are both positive displacement superchargers, and the centrifugal type is dynamic.