FYI- 5yrs ago when i raced, my Nova Rossi CX12 (6port, parisdished head, MatrixMods resleeve and build to .14ci) made 4.2hp@41000rpm on 60%.
That engine stock made 1.2hp on 20%. It was intended for a RS4... 4wd on-road car, but i used it in a custom built RC10GT (no factory parts, complete from aftermarket). It only weighed in at 3.93 lbs (for races only) according to the scale at Full Throtle(dunno if thats still open or not).
Those lil engines can make some retareded amounts of power in the right hands. With the right tuning in the carb, you can get good run time too. I had a OS CV.12 that ran 24min on 2.5oz of fuel. Thats about 8 or 9min longer than 95% of the guys that run.
I fed the Nova Rossi with a 6v fuel pump for a plane... thats right, i turned it to fuel injection. It was fed air thru a .21 ducted fan engine on a 9v system spun by a Reedy FireHawk motor. Thats right again... i turned it forced induction.
Now with this set up it made its 4.2hp... but it also added an even 4 lbs to that 3.93 lb raceweight.
So even at 7.93lbs, it made 4.2hp...
1.8lbs/hp