To enable non-throttling operation of gasoline S.I. engine, we have manufactured engines equipped with a newly developed Hydraulic Variable-valve Train (HVT), which can vary its intake-valve closing-timing freely. The air-intake control ability of HVT engine is equivalent to conventional throttling engines. Combustion becomes unstable, however, under non-throttling operation at idling. For the countermeasure, newly designed combustion chamber has been developed. The reduction of pumping loss by the HVT depends on engine speed rather than load, and amounts to about 80 % maximum.A conventional engine-management system is not applicable for non-throttling operation. Therefore, new management system has been developed for load control. The vehicle equipped with the HVT engine proved an equivalent driveability to the vehicle with conventional engine, particularly, it satisfied EPA emission standards in the U.S. and proved about 7% improvement of fuel consumption in EPA Urban Dynamometer Driving Schedule.