LSPI is an important issue to enable and enhance the effect of downsizing in SI engines. Experimental work was carried out by using 4 cylinder turbocharged gasoline engine, attaching the extra supercharger to get a higher boost pressure. Many parameters of driving condition, engine specification and lubricants were studied and some of them were extracted as the major items which affect the possibility of LSPI. Coolant temperature and Calcium (Ca) additive to lubricant had strong effect on the frequency of LSPI. Combustion strategy of strong miller cycle and LPEGR were also studied and compared in very high BMEP condition. Finally IMEPg of 3MPa at 1500rpm was achieved by using a single cylinder test engine equipped with 2-stage mechanically supercharged intake system.