VGT TECHNOLOGY

A Variable Turbine Geometry turbocharger is also known as a variable geometry turbocharger (VGT) or a Variable Nozzle Turbine (VNT). A turbocharger equipped with Variable Turbine Geometry has little movable vanes which can direct exhaust flow onto the turbine blades. The vane angles are adjusted via an actuator. The angle of the vanes varies throughout the engine RPM range to optimize turbine behavior.

In this cut-through diagram, you can see the direction of exhaust flow when the variable vanes are in an almost closed angle. The narrow passage of which the exhaust gas has to flow through accelerates the exhaust gas towards the turbine blades, making them spin faster. The angle of the vanes also directs the gas to hit the blades at the proper angle.

This cut-through diagram shows the exhaust gas flow when the variable turbine vanes are fully open. The high exhaust flow at high engine speeds are fully directed onto the turbine blades by the variable vanes.

Variable Turbine Geometry has been used extensively in turbo diesel engines since the 1990s, but it has never been on a production petrol turbocharged car before until the new Type 997 Porsche 911 Turbo. This is because petrol engine exhaust gases are allot hotter than diesel engine exhaust gas, so generally the material used to make VTG turbo could not stand this heat. The 997 911 Turbo uses a BorgWarner VTG turbocharger which uses special materials derived from aerospace technology, hence solving the temperature problem.