This experimental investigation is an initial step in separating the influences of swirl and inducted kinetic energy on combustion in a homo - geneous charge engine. By rotation of the intake port about the axis of the intake valve, the swirl ratio was varied from zero to 2,8 while maintaining constant intake port flow, and hence constant inducted kinetic energy. Combustion data were obtained at a low speed, light load operating point (1500 RPM/60 psi IMEP) with MBT spark timing. The effects of the increase in swirl were a 25% decrease in ignition delay, a 10% decrease in combustion duration, and a significant improvement in combustion stability. Estimates were made on the effect of swirl on turbulence intensity (10% increase) and integral length scale (10% decrease). Both the increase in swirl and the use of a near-central spark plug location improved the lean operability. This enabled the ISFC to be reduced by more than 11% compared with the case of peripheral spark plug and zero swirl at equal combustion stability. In this comparison, the reduced ISFC via lean operation was accompanied by a decrease in ISNOX from >16 to 0.4 and an increase in ISHC from <1.9 to 6,8 gm/IHP-HR.