Kerry,


It is an OS.90FSR.

This is a beast, power-wise, compared to current .90-.91 engines, with larger intake bypasses.
The current OS.91FX engine is a bored and stroked OS.61FX, with narrow intake bypasses, which limit its high end power.

This engine is, however, significantly heavier as well.


The strange thing is that the ASP (Sanye China) clone of the OS .91 engine uses a 20 mm diameter crankshaft, like the even larger displacement sibling of your engine, instead of the 17 mm crankshaft of your engine... giving it even more power potential through its much larger crankshaft gas passage.