Internal combustion engine development is mainly driven by new emission regulations and fuel cost. The introduction of hybrid power trains allows the development of highly efficient non-traditional internal combustion engines. One way of increasing thermal efficiency while avoiding issues like high mechanical stress or knock, is to realize different expansion and compression strokes. Different solutions exist such as the Miller/Atkinson cycle or the five stroke engine.A 5-stroke turbo-charged port-injection spark-ignition engine has been developed in the present study for use as a range extender or series-hybrid main power source. Its development and design are based on 0D/1D model and experimental results have been compared with the engine model. The 5-stroke engine is a three-cylinder in which two cylinders, called high pressure (HP) cylinders, perform a four-stroke cycle with a volumetric compression ratio of 8:1 and alternatively a second expansion of the burnt gases is performed in the third cylinder, called low pressure (LP) cylinder with a volumetric compression ratio of 30:1, the overall expansion ratio being 12.7:1.The boost pressure delivered by the turbocharger is controlled by a particular innovative system called “smart wastegate”, consisting in two differently controlled exhaust valves, one feeding the turbine, the other bypassing the latter.The engine develops 32.5 kW for an engine of 4000 rpm. BSFC is 226 g/kWh which corresponds to a global efficiency of 36.1 %.The engine parts and technology are standard and allow cost effective development of the concept as no special component with special development is needed. Moreover, the version studied consists of a multi-point port-injection system and a two valve combustion chamber.