Incorporating lean burn engine technology has been considered as one of the most promising methods for improving fuel economy and reducing emissions. There has been, however, difficulity in expanding the compatibility region, where both the extension of LML(Lean Misfire Limit) and the reduction of NOx are simultaneously achieved while keeping satisfactory drivability.The lean misfire limit has been extended by the introduction of swirl and tumble motion. Three types of ports with an IACV(Intake Air Control Valve) have been developed to satisfy seemingly contradictory requirements of obtaining sufficient swirl and tumble motion to improve combustion and still keep high volumetric efficiency.Effects of newly designed ports with IACV on LML, emissions(NOx, THC, CO), BSFC, MBT, were confirmed in a four cylinder engine. Tests showed that the combustion duration was shortened and consequently lean misfire limit and EGR tolerance were improved. Emission level of NOx is considerably reduced.