ORIGINAL: airraptor
even a 8x4 is to big of a prop for a stock engine. i would go with an 8x3 if the plane is heavy or run a 7x4 an 8x5 is way to big. i know guys that run 8x5's on their OS .25 ax/fx
8-4's are fine on a .15, but are the most load I would put on one. They run at decent if not excessive rpm and none of mine have ever showed signs of overheating or distress, plus performance is good in larger/draggier/heavier aircraft. I am not one to put excessive loads on an engine btw. But on something smaller and zippy let it spin - 7-4, 7-5 perhaps.