Exhaust gas turbochargers are provided on an engine to deliver air to the engine intake at a greater density than would be possible in a normal aspirated configuration.  This allows more fuel to be combusted, thus boosting the engine's horsepower without significantly increasing engine weight. 
Generally, an exhaust gas turbocharger includes a turbine section and a compressor section, and uses the exhaust flow from the engine exhaust manifold, which enters the turbine section at a turbine inlet, to drive a turbine wheel located in the turbine housing.  The turbine wheel drives a compressor wheel located in the compressor section via a shaft that extends between the sections.  Air compressed by the compressor section is then provided to the engine intake as described above. 
The compressor section of the turbocharger includes the compressor wheel and its associated compressor housing.  Filtered air is drawn axially into a compressor air inlet which defines a passage extending axially to the compressor wheel.  Rotation of the compressor wheel forces pressurized air flow radially outwardly from the compressor wheel into a compressor volute for subsequent pressurization and flow to the engine.