In this work, through the utilisation of a thermodynamic numeric code, ,it has been studied the possibility to introduce an heat exchanger to transfer the residual enthalpy present inthe exhaust gas of a .piston engine to a compressor-turbine system. Different configurations -have been considered, but the most promising of them, under the point of view of the specific power, seems to -be that in which a conventional exhaust gas power turbine engine (compound) is coupled with a turbogas -system .that receives energy by an heat exchanger. In fact the numerical analysis done :.has shown as the .temperature of gas from the piston engine, also after it has been completely expanded in a,power turbine, 4s considerably high; high enough to transfer an amount of energy through an :heat ..exchanger sufficient to get power by the compressor-turbine system joined to the engine. The main difficulty.at the moment is represented by the weight and dimensions of such a system. However it is -easytoaimagine that present improved technology will be able quite easily to solve this problem.