James G.

Thank you.

WW,

If you mount an engine that would make approximately 3 HP at about 16,500 RPM and more at higher revs, like a dedicated ducted fan engine, you would be spinning a 10x10 at this 16,500 RPM.

The Rossi .65 is a dedicated 12K peak engine. The manufacturer claims a very doubtful 3.8 HP at 12K for this engine.
Going to 16K with this engine, will get you no where.
I somehow find it difficult to imagine this engine, spinning a 14x9 at this RPM, when an MVVS .77, with the tuned silencer can manage 12,200 only on a 12x8, or a 13x6.

The Rossi .65 is a similarly tuned engine with 17% less displacement, that cannot possibly achieve over twice the volumetric efficiency, of its peer. 12,200 RPM on a 12x8 prop is VERY respectable performance. The highest number in the MAN .60s shootout, on this prop size (the Fox Eagle), could only manage 10,950, which is nearly 28% less HP absorbed.

The beginning 80s F3A engines, tuned to 14-16K are invariably full length pipe equipped, which moves the CG back, when compared with a short muffler engine.