A turbocharger is a relatively simple device composed of three sealed chambers. The first two contain a turbine and between them is a third, sealed, oil-filled chamber through which runs a shaft connecting the two turbine's (see accompanying diagram) After exhaust gases leave the cylinders, they pass into one of these chambers - the "hot side" - spinning the turbine. The greater the volume of exhaust gas, the faster this turbine spins.

As the hotside turbine spins, it spins the turbine in the opposite chamber, or compressor side. As this compressor spins, it draws in outside air and forces it into the engine intake manifold and finally into the combustion chambers. When the turbine reaches sufficient speed, it forces so much air into the cylinders that the pressure there exceeds atmospheric pressure. At this point the turbocharger is said to generate boost, which is usually measured in pounds per square inch (psi) or atmospheres (bar). The turbocharger thus pumps additional air into the cylinders, which means the engine can burn more fuel, which in turn means it produces more horsepower.

The turbocharger’s main advantages are its light weight, mechanical simplicity, durability, and the and fact that it uses waste energy - engine exhaust - and not engine horsepower. Moreover, since the volume of exhaust gas is dependent upon engine load, the turbocharger comes into play as needed. The greater the load, the more the turbo boast.

While mechanically simple, turbochargers are nevertheless precision devices. They must withstand temperatures greater than 800 degrees Fahrenheit and shaft speeds as high as 100,000 rpm. That means proper lubrication of the turbocharger shaft bearings is crucial. Any loss of oil pressure or failure of a shaft seal can produce failure in seconds.

As a turbocharger compresses air, it also heats it to as high 300 degrees Fahrenheit, making it less dense. To reduce this and get more air into the cylinders, many turbocharged engines are fitted with an intercooler or after cooler. This is basically a radiator located downstream of the compressor side, inside of which circulates either engine coolant or raw water. As the air passes over the unit’s fins, much of the heat is removed. Not only does this make the air denser, but it also helps reduce the temperature of components inside the cylinders.