In developing high speed swirl supported direct injection diesel engines it has been a general experience that different engine results (performance, smoke and emission) may be obtained when using different intake port designs, although the swirl numbers (stationary flow test rig) of the different ports were identical. Therefore, an in-cylinder flow investigation under motoring conditions using hot wire anemometry was performed for three different inlet port designs having the same swirl number. Special emphasis was drawn on the engine design parameters being as close as possible to reality. Thus, the flow investigation and the engine tests were carried out at a typical compression ratio of 18 : 1 using a standard combustion bowl in the piston as well as produceable inlet ports. All flow measurements were carried out under motoring conditions covering the speed range from 1100 to 2400 rpm. By use of probes located on the piston a two-dimensional flow field including turbulence parameters could be established throughout the whole cycle. In parallel engine tests were carried out with the ports in question in order to obtain performance, smoke and gaseous emissions data with these ports. Hence, engine test data could be linked with in-cylinder flow data. As a result certain air motion characteristics within the bowl were found to be essential for the magnitude of smoke in the exhaust and for the efficiency of combustion (fuel economy).