The piston with high compression ratio and late IVC were combined in order to improve the fuel consumption with maintaining the peak firing pressure lower than the mechanical constraints. In addition, the change in the combustion process was investigated by using numerical calculation to find the emissions deterioration process with higher compression ratio. From this investigation, revised combustion chambers were designed in order to improve the exhaust emissions characteristics. As the results, it is not only numerically but also experimentally confirmed that combination of retarded IVC timing and one of the revised combustion chambers can achieve remarkable improvement in both exhaust emissions and fuel consumption.