system when the engine is operated at a constant speed in this example a drop in turbine isentropic efficiency of 8 percentage points is predicted between turbine operation with wastegate shut and with wastegate open for the same total mass flow rate this is energy that cannot be recovered by the lp turbine the efficiency of the electrical machine 70 as a generator may be significantly greater than that of the wastegate or other diversion mechanism although likely less than 100 efficiencies of typically greater than 95 can be reasonably expected especially for low speeds at higher speeds the efficiency of the electrical machine 70 may be reduced implementation of the electrical machine 70 on the low pressure turbocharger stage 60 rather than the high pressure turbocharger stage 40 is beneficial to the overall system efficiency lower rotational speed in the low pressure turbocharger stage 60 imply greater efficiency of the electrical machine 70 as discussed above for example a 13 percentage point improvement in efficiency may be possible by dropping from 140000 rpm to 80000 rpm efficiencies greater than 90 may be reasonably expected which is a significant improvement in comparison with previous wastegate operation referring next to fig4 there is shown a diagrammatic view of an engine system for use with a turbocharger system the engine system may comprise an engine 80 the turbocharger system 10 a controller 90 and a sensor 95 the engine 80 may provide exhaust gases to the exhaust gas inlet 20 of the turbocharger system 10 the turbocharger system 10 may then provide compressed air through compressed air outlet 33 the pressure of the compressed.