Re: prop ?
Your question cannot be answered. Props don't make power, the engine does that so installing a "bigger" prop doesn't make the engine more powerful. In fact it may make the rig perform worse because the engine cannot twist that big a prop.
While you gave us lots of detail about the engine, that info is worth nothing since we don't know what prop you have now (diameter and pitch), what kind of boat this engine is installed on (yes -- we know its aluminum -- but what kind) and what is the wide open throttle rpm is with the current prop. Wide open throttle rpm is what you actually see on the tach, not what the manufacturer recommends. When selecting a prop you want one that obviously fits the engine, but you want pitch selection that allows the engine to run at the top of the engine manufacturers rpm band. Speed will be whatever that prop provides.
