Don't confuse noise with power. If it revs higher RPM, this may not be indicative of power increases, and may, in fact, hurt the engine. Use the recommended prop for that engine. If the plane came with a particular size prop, stick with it unless you really know what you are doing or if someone with a lot of experience helps you out. Don't try to make this plane do something it was not designed to do by trying to over or under prop'ing it.

CGr