Our airframes are approved for nearly any engine in a certian weight and hp (65-150hp) limit but Rotax and Jabiru are the most widely used followed by types like Revmaster, Aerovee, some volkswagen engines, Subaru EA81, Toyota Yaris 3 cyl, Rotec radial, UL Power, D-motor, Continental, Lycoming 233 to name but a few I can think of.