Downsizing has nowadays become the more widespread solution to achieve the quest for reaching the fuel consumption incentive. This size reduction goes with turbocharging in order to keep the engine power constant. To reduce the development costs and to meet the ever tightening regulations, car manufacturers rely more and more on computer simulations. Thus developing accurate and predictable turbocharger models functioning on a wide range of engine life cases became a major requirement in industrial projects.In the current models, compressors and turbines are represented by look-up tables, experimentally measured on a turbocharger test bench, at steady point and high inlet turbine temperature. This method results in limited maps : on the one hand the compressor surge line and on the other hand the flow resistance curve behind the compressor. Mounted on an engine, the turbocharger encounters a wider scale of functioning points. Using only the actual compressor and turbine maps in an engine simulation is sometimes a limiting factor.For this paper a specific experimental campaign has been performed with different automotive turbochargers on a test bench in order to expand the measured iso-speed lines. On the compressor side, new measurements methodologies are describedinto the choke area, up until a ratio of 0.8,beyond the surge line, into the negative mass flow rate.The results are used to establish semi empirical models of the compressor power in these areas and to study the surge loop amplitude.