Ok guys, I have a st40 ringed engine. The prop sizes that ST. gives is a 9x7, 9x8, 10x5, 10x6, 10x7, 11x4, and 11x5. My question is witch size will give me the best results. I need the most or best power I can get out of this engine, the engine is a little under sized for the project.. thanks again.