If a car is going to use a series hybrid or extended range EV powertrain a a conventional piston engine is hardly the optimal package for a range extender. Something smaller and more power dense would be preferred. A small turbine engine is one possibility and that's exactly the approach taken by Langford Performance engineering. They've used a micro-turbine from California-based Capstone Turbine. A turbine works well in this type of application because it can run at constant speed.