While turbocharging already combines high specific rated engine power with low fuel consumption, there is still potential for optimization to achieve prospective demands for fuel efficiency with low emissions. Using engine exhaust energy, the turbine underlies pulsating flow conditions from high towards zero mass flow at almost constant blade speed. The average turbine efficiency is then affected for the high blade to jet speed ratio conditions, which is very important at low engine loads during urban driving conditions. Since turbocharger performance is very sensitive for the overall engine efficiency, a very accurate measurement of the characteristic maps is desired to evaluate the thermodynamic behavior of the turbocharger and to ensure best possible matching. This paper presents a methodology to extend the turbine performance at low expansion ratio and to characterize the adiabatic efficiency in a wide operating range. This enables measuring turbines on a hot-gas test bench at very high blade to jet speed ratio and very low turbine flow to develop, improve, and validate reliable turbocharger models that can be used for full engine simulations. The industrial applicability has been proven from very low turbine power up to negative turbine power output simply based on using inlet guide vanes (IGV) upstream of the compressor. By generating a swirl in the compressor wheel rotating direction and pressurizing the inlet air, the compressor can be run as a turbine. Thus, the compressor provides power to the shaft and the turbine can be driven with very low flow power. The test campaign has been realized under quasi-adiabatic conditions to limit the heat transfer. While measuring at three different oil temperatures, the impact of remaining internal heat transfer has been taken into account. A turbocharger heat transfer model has also been used to correct residual heat flows from the obtained data set for all oil temperatures.