The engine manufacturers aren't lying about horsepower, but they are misleading you. Given torque in foot-pounds, horsepower is torque times rpm over 5252. The torque curve of a typical model engine is a fairly shallow rise and decline so the horsepower tends to be aligned with rpm. This is how boat and ducted fan engines put out so much horsepower, they turn extremely high rpms.

If you read carefully the .61 engine comparison in Model Airplane News by Dave Gierke, you would have noticed that all of the .61s tested were putting out about 1 horsepower at the rpm of a sport prop, 10,000-12,000 rpm. This is a far cry from the nearly 2 horsepower claimed by some .46 sized engines.

The fact is, just about all sport engines put out very close to the same power on the same prop and same fuel. In my opinion, there would be as much difference in individual engines of the same make as there would be between different brands.

Given the above is reasonable, the best power-to-weight ratio would be with the lightest engine. If you are talking .46s, they all weigh the same so you are talking very small differences. I own, or have owned, several different brands of .46 size engines. Personal preference, ease of tuning and mid-range performance is really the only difference. Right now I have OS, Magnum, GMS, & Thunder Tiger. I had Fox, Rossi, K&B and MVVS.

I see the same thing for .61s and .91s.

When it comes to 4-strokes, YS makes the most power. As for the others, you can cover them with a small towel. The only difference I see is the Saitos, in particular, the .72 and .91s, are lighter. I would think this is the reason Saitos are seen a lot in fun fly planes. The Saito .91, for example, is only 3 ounces heavier than a typical .46. Many profile fun fly planes need nose weight with a .46 so a much more powerful Saito .91 makes an excellent choice.