A friend's father had one of these - http://www.tractorda...ere-b-engine.html

16 horsepower. 6.8 mph in 4th.

But it had a mountain of torque because it had two pistons that were about the size of trash cans. ;-)

Yeah, gearing can do a lot, but there are lots of advantages to big, slow motors in those applications.

Cheers,
Scott.