A new empirical model is presented to simulate the complete performance map of an automotive turbocharger which consists of a radial turbine and radial compressor. Each of these components is modelled by a particular system which includes basic elements such as orifices, diffusers and a head gain unit organized in series or in parallel. This model which is, in particular, practical for detailed computer program of engine simulation may be simply calibrated to reproduce a wide range of experimental performance maps of typical automotive turbochargers. The isentropic efficiency contours of each component have been approximated by a generalized mathematical expression. The relevant constants may be adjusted so as to fit a specific map.