Since the late 1990s many diesel vehicles have a Variable Geometry Turbine (VGT) or Variable Nozzle Turbine (VNT) turbo fitted. These turbos minimise turbo lag, improve throttle response at low speed and provide much improved torque.
Most commonly, the design utilises a ring of moveable vanes around the turbine wheel to change the speed and direction of the exhaust gases acting on the turbine wheel. At low speeds the vanes move closer together which accelerates the gas flow onto the turbine wheel. At higher speeds the vanes open wider to prevent the turbo over boosting.
Despite these benefits, turbos can be prone to problems, which include: