I bought a rossi .81 used in good shape ran like a champ. I had it in my Skyburner 60 that I scratch built from M.A.N plans with a ramtec fan unit and an unknown muffled pipe. I was running omega cool power 5% with 5 oz synthetic and 2 oz castor oil added on an OPS cold plug. When I tuned the pipe it maxed out at 19,700 rpm. Not rich, not lean, nice fat smoke trail, just right, ran like a champ. I had been flying all day yesterday and all day today. It was running great and hauling balsa. On the last flight of the day I was flying along and the engine started to run a little rich. So I banked hard left and came out of the turn in a dive to make a high speed pass to see if would lean out. It started to lean out a little and then poof, like it ingested something. It was still running although very rich, lots of smoke trail. I throttled back to half, dropped the gear, and made an emergency landing. When I chopped the throttle on final the engine died. When I got it back to the pits I found the sheared impeller shaft.

What happened?
Did I do something wrong?
Or is this a common problem with rossi engines?
Does anyone still sell the OS .91 vrdf?
If not, will the OS 46 vrdf work in a ramtec fan unit?