ONE OF THE most severe problems of the automobil industry at the present time is to offer well optimized products in the market at the right time due to the very rapidly changing consumer demands.To save time and cost during the predevelopment phase it is helpful to optimize the engine and power train concept by measures of theoretical simulation, whereby a number of influence parameters can be varied in a very short time. This paper describes an engine simulation model, which estimates the friction as well as the combustion patterns depending on principle design parameters like bore, stroke, number of main bearings, and number of cylinders etc. Combining friction and combustion results, the model leads to a map of BSFC. In a second step this map is used to estimate the fuel consumption of different engines in cars for different test cycles. Results of the influence of swept volume on the car mileage will be given. A comparison of calculated and experimental results shows good agreement.