Results from the 1600 cm3 PCI- (PreChamber Injection) Stratified Charge Engine with a divided combustion chamber and fuel injection into the prechamber were described in SAE Paper 750 869. The main objective of continued development on this engine was to meet future emission and fuel economy standards for European countries with a simpler concept than required in the US, but equally effective. This work lead to the lean burn PC- (Pre Chamber) engine, where the prechamber fuel injection system is omitted.The main part of the program was concerned with the optimization of the PC-Combustion Process, however, the effects of the engine periphery were also considered in detail.A large number of combustion chamber parameters were thoroughly investigated on a 1300 cm3 four-cylinder water-cooled inline engine. Ignition system parameters were included in the test program because they can significantly influence the combustion process. Since an engine concept had to be developed, a large part of the experimental work dealt with fuel-air-mixture formation, distribution and heating. A simple means of exhaust gas after-treatment was also considered in the concept.Exhaust emissions and fuel consumption were evaluated in a number of vehicle tests according to European test procedures. Results show that future European exhaust emission standards, if not too severe, are likely to be met without catalytic after-treatment. No significant problems have been encountered thus far, however, more durability testing needs to be done.