An engine model for use in computer simulation of transient behavior in drivetrain and vehicle systems is presented. Two elements, important for deviation (e.g. turbo-lag) from steady state characteristics, are the inertia of the supercharging unit (turbo shaft) and the fuel injection control system.No extensive combustion calculations are carried out within the model. Instead it uses condensed results from existing combustion models and measurements. The model is semi-empirical. Some of the engine specific properties needed for simulation are (e.g. for a turbocharged diesel): engine data in steady state operation, mappings of compressor and turbine performance, inertia of the engine components condensed to the crankshaft, turbo shaft inertia, displacement, compression ratio and the essentials of the fuel injection control strategy.Input parameters to the computer program based on the model are accelerator pedal position and external torque acting on the flywheel. Output properties from the program are engine torque, speeds, temperatures, pressures and emissions.In a typical downshift operation the delivered torque can instantly deviate by 30% as compared with steady state operation. It can be concluded that this model might be a useful tool for heavy vehicle drivetrain simulation.