very rare os .61 fsr,ringed,has original paperwork,box,came from os with perry pump,and three needle perry carb! these were only limited production engines,they have high rpm,lots of power! engine does not come with muffler,came that way so you could choose a tuned pipe,or muffler! this engine would be great in the new great planes dirty birdy arf,or horizons new pheonix vintage pattern planes! these engines were top of the line for pattern in late 70s,early 80s.engine is short stroke.