In order to meet stringent government emissions standards without penalizing the fuel economy of gasoline engine cars, a number of alternative engine concepts have been investigated. This paper describes a research investigation and parallel development activity on prechamber stratified charge engines. Single-cylinder engine investigations are first described. Alternative design and operating parameters are investigated and compared in these engines. Design and development of two multicylinder engine designs incorporating prechamber 3-valve configurations is next described. Finally, a car development and evaluation program is outlined, using both small and large cars with alternative engine configurations and after treatment devices. Results of the above prechamber stratified charge engines are compared with conventional engines in order to assess and evaluate the emission and economy potential of this type of engine. The authors conclude that this type of stratified charge engine possesses NOx emission and fuel economy performance similar to a conventional engine but at a high HC emission level.