First of all, the HP rating is pretty much a fable. This is a projected horse power rating based on the ability to even reach that RPM. Unfortunately, with most of these engines, to efficiently run, the prop necessary is usually larger than ones that would even allow attainment of 16K rpm. The actual RPM range is about in the mid 12's for 40 - 46 engines and goes down from there.

And at that RPM range, the prop noise would be just about unbearable.. and the engine would probably not last very long.

Now some will, some are designed for that RPM range, but not the general collection of sport engines produced by Super Tigre, OS, Evolution, and others.

The advantage of the larger engine is usually in the power or torque that it generates. The larger mass of a larger prop will usually result in more torque, usually more horse power. As you cans see, HP ratings are subjective. Larger engines will generally produce more power.. in the form of torque and will turn larger props much easier.

The OS AX series has a needle valve that is located at the carb but is rotated so that it points rearward giving access to it much easier than when they are perpendicular to the prop shaft and carb. Fingers don't get abused when they are angled back like that.

With rear mounted needle valves, the obvious advantage is that they get your fingers away from the prop. The bad part is that they are usually made of plastic and can break easily. Another disadvantage is that they take up space behind the engine which, in some models, may not be at a premium.

CGr.