blue moon--14 X 8 three blade will be too much for the 100. a 14 X 8 two blade is right at the limit for this engine. If you are running a 15 X 8, then I suspect (actually, I know by experience) that you are lugging this engine too hard. A 13 X 7, 13 X 8, or so would be a nice fit for the saito 100. I too have had decent experience with three bladed props.