Variable geometry turbochargers include turbines that move to change the output of the turbochargers. The moveable turbines address the power needs of the turbochargers at part load operation. For example, as the load placed on the engine that is partially powered by the turbocharger changes, each of the turbines or blades of the turbocharger can move to change the speed at which the turbocharger rotates. This change in rotational speed changes how much air is forced into the engine, thereby changing how much power is generated by the engine.
This type of turbine design avoids the need of using waste gates and can improve engine efficiency by reducing pumping losses associated with an undersized turbine on air handling systems. The variable geometry turbochargers, however, also are expensive and less reliable than other turbochargers due to the large number of moving components.