VGTs

Variable geometry turbochargers (VGTs) are a type of turbocharger in which the turbine side has adjustable geometry. The turbine housing contains a set of moveable vanes around the turbine wheel; by varying the vane angle, the effective inlet area to the turbine can be increased or decreased. This allows the turbine to respond over a wider range of engine speeds than a fixed-geometry turbocharger.

VGTs are controlled by the engine management system using actuators—typically hydraulic or electric—that move the vanes in response to signals such as engine speed, load, boost pressure, and temperature. In many systems the vane position is monitored by sensors and adjusted in a closed loop to maintain target boost and prevent surge.

The main advantages of VGTs include improved low-end torque and quicker throttle response, reduced turbo lag, and more efficient operation across a broad RPM range. They can deliver higher peak boost without increasing pumping losses, which can translate into better overall efficiency and, on some designs, lower emissions.

Drawbacks include increased mechanical complexity, cost, and potential reliability concerns with the vane actuators, bearings, and sensors. Soot buildup, oil contamination, or vane sticking can cause reduced performance or malfunction, sometimes triggering limp modes. They are most common on diesel engines but are also used on some gasoline engines. Maintenance and proper lubrication are important for longevity.