3-blade props at high RPM's like we have in model engines actually loose some of their efficiency. The higher the RPM may not be the rule with a 3-blade, try to keep your RPM around 9800 and you will get the most thrust out of it. The 1 inch rules doesn't always work because of it. If you are using a 2-stroke the power band may require you to run at a higher RPM than 9800 but I would give it a try. I use 14x7 3-blade MA props on my .91 4-strokes and they turn at 9800+ with 15% fuel. Plenty of thrust! I ran 8-6 3-blades on my .30 4-strokes and got 11,000 rpm from them but they stopped giving anymore thrust at around 9800 just like the bigger props. Hope that helps a little.