When comparing automotive and large-bore diesel engines, the latter usually show lower specific fuel consumption values, while automotive engines are subject to much stricter emission standards. Within an FVV (Research Association for Combustion Engines) project these differences were identified, quantified and assigned to individual design and operation parameters. The approach was split in three different phases: 1Comparison of different-sized diesel engines2Correlation of differences in fuel consumption to design and operating parameters3Further investigations under automotive boundary conditionsThe comparison in the first phase was made on the basis of operating data and energy balances as well as the separation of losses based on the thermodynamic analysis. To also determine the quantitative effects of each design and operating parameter, a 1D process calculation model of the passenger car engine was transformed gradually to a large-bore engine in the second phase. The advantage of the large-bore engines results basically from their higher combustion air ratio, shorter combustion duration, lower wall heat losses and high positive gas exchange work due to a high turbocharger efficiency.Experimental tests showed that the benefits in fuel consumption of the large-bore engine can be transferred to an automotive engine by applying a scaled-down large-bore engine combustion process. The tests showed further that it is crucial to provide the high combustion air ratio of the large-bore engine with sufficiently high turbocharger efficiency and that the large-bore combustion system is much more sensitive to the air ratio concerning smoke emission.