ORIGINAL: Rudeboy
The engine was intended for a prop jet... the heaviest prop it is going to see is probably an 11x9!
The 11x7 is a break in prop, and suits the engine just fine: turning up to 14,000 rpm... while still rich. It is a ringed engine after all.
Winibald,
In the 70s and up to about 1982, before RPM was pulled down by larger props and longer pipes, the better F3A .60 piped engines, used to spin an 11x7, 11x7.5or 11x7.75 prop at 14,500-15,300 RPM. So having a .90 engine spinning this size prop at this RPM, albeit rich, is nothing special.
If it is an engine intended for very high RPM (CMB, Picco, OPS, Rossi, Jett), it should show close to 16K on this prop size.
Now it becomes a blade throwing risk...