For gas engines, consider the RCS/Moki 1.40 or the MVVS 1.60 engines. Both will fit in the nose of models that will accomodate a 1.20 four-stroke glow engine. Both cost approximately the same as a 1.20 four-stroke glow engine and weigh nearly the same.

What little more cost may be involved in buying an optional muffler will be quickly offset by the huge reduction in fuel costs.