The turbochargers of the two S-Class CDI models electrically adjust the pitch of their guide vanes in accordance with the engine speed in order to use as much exhaust gas as possible for compressing the intake air and developing boost pressure. This type of design is known as VNT (variable nozzle turbine) turbo-charging.
The system ensures optimal control of boost pressure in all driving situations: at low engine speeds, the guide vanes reduce the cross-sectional area of the exhaust gas stream and boost pressure is increased; at high engine speeds on the other hand the cross-sectional area is increased and the turbocharger operates at a lower speed.
Thus in all situations, as much energy as possible is derived from the exhaust gas stream for generating boost pressure. Better cylinder charging and thus higher torque are further advantages of VNT turbochargers.