The internal combustion engine (ICE) for a series hybrid vehicle must be very compact, fuel efficient reliable and clean; furthermore it should possess excellent NVH features; finally, the cost should be as low as possible.An unconventional but not exotic solution, potentially ideal to fulfill all the above mentioned requirements, is represented by a 2-Stroke externally scavenged GDI engine, without poppet valves. BRC (Cherasco, Italy) and PRIMAVIS (Turin, Italy) are currently developing an engine of this type, incorporating a patented rotary valve for the control of the charge induced to cylinder. The development is supported by extensive CFD simulations, which are able to predict all the main engine performance characteristics.The paper analyzes, from a theoretical point of view, the installation of the engine on an electric vehicle, previously optimized for a small Diesel engine (Smart 0.8 l CDi). For a straight comparison between the Diesel and the 2-Stroke GDI engine, all the vehicle components are the same. Furthermore, the operating points employed for battery charging correspond to the same values of brake power.The 4-S Diesel and the 2-S GDI engine are compared from several point of views: fuel economy in the European driving cycle, capability to comply with stringent emissions regulations, cost, overall dimensions, weight, etc. It is found that the new 2-Stroke engine can possess the advantages of the Diesel in terms of fuel efficiency, while maintaining the compactness and cost effectiveness of the best SI Range Extenders.