Yes, there are folks doing it. Richard Sohn has been working on his single rotor for years, it's running now. With PSRU, exhaust, coolant, radiators, etc I think it weighs a tad over 200 lbs and I think he plans to get about 90 HP out of it. That's output that should be good, continuous "we can do this all day" HP (decreasing, of course with altitude in this normally aspirated engine).another thought is convert a mazda 13b to single rotor. plenty of readily available parts out there to do so.
Charles, did you ever determine the true horsepower of this motor? I'm really curious about it.i know, im going to mount the motor on my test wagon roller and put an adjustable prop on it and check the pull thrust before mounting it on the minimax.the minimax weights 172 lbs with no motor. these wankles were put in artic cat panthers snowmobiles and they are prized for there pulling power , they are used by ski lodges (now) to pack fresh snow trails 3 foot high that other snowmobiles cant handle.and pulling 600 to 800 lbs of fire wood on a sled with no problem. i really think this motor is 35 to 40 hp or more.it weighs 32lbs with exhaust and i can cut more weight off of it .it will also run of off kerosene that i thought was kool.its in new condition now.it will run off of points or electronic ign i installed.that 20 hp was rated in 1972 .ratings back then were different than now.