System Components

The 2-stage sequential variable geometry turbocharger: 

uses a turbine wheel that is similar to a conventional turbocharger but with a different turbine housing to accommodate one turbine and 2 compressor impellers. That means that there is one turbine and two impellers. One impeller is designed for low speed operation and the other is for medium to high speed operation, providing the functionality of a twin turbo in a single turbocharger. There are two separate air inlets, one for the low speed impeller and the other for the high speed impeller. There is a wastegate and wastegate control valve. The turbine housing contains hydraulically actuated and electronically controlled vanes that control the effective size of the housing.

The single-stage variable geometry turbocharger: 

uses a single impeller and a single turbine without a wastegate actuator or wastegate control valve.

Turbocharger wastegate actuator (if equipped): 

when the boost pressure reaches a predetermined value, the turbocharger wastegate control valve opens allowing vacuum to open the turbocharger wastegate actuator.

Turbocharger wastegate control valve (if equipped): 

when the turbocharger wastegate actuator opens some exhaust bypasses the turbine and flows directly into the exhaust system limiting maximum boost and back pressure.