RE: OS 91 VRDF experts wanted
This is a OS .91VRDF pipe. It is 18. 5 inches (45.72 cm) long and the major diameter is 2 inches (5.08 cm) with a ruler for scale. This pipe is pretty big compared to the one you have shown so I would go along with the assessment that your is for a .60 size engine which would explain the high pressure you mentioned. This pipe is for use with a os.91vrdf with a dynamax 5.25 df unit and should spin a 10" prop to at least 22k rpm. And I would also add that I don't think a wood prop is a good idea at that high of a rpm as mentioned before.
You should not run that engine with lower than 22% oil content!
As far as nitro I know they run good on 10-15 %, as far as what type of tricks can be done to the engine I'm not sure, but it is my understanding there are a lot of mods that they can handle.
I edited to correct the measurements...
It is my understanding that these engines used with a remote needle valve setup (in flight variable) can spin up even higher with a prop and a tuned pipe.