I could be wrong but I think that the new Stihl 4 stroke is one of them. It's used in the back pack leaf blowers (and probably their other products) and has some guts! Not sure who else, but chances are the lawn maint./landscapers are going to be the ones who prove whether these engines are reliable. Don't know if the Stihl engines could be converted to bike logic or even if they would be practical, but I'd be interested in finding out.