RE: RE:
11X12, 12X8, 12X9 APC or 12X8 S-2 MAS seem to work well on a tuned muffler or tuned pipe and should work with the stock muffler with or w/o baffle. I've tried those on my Phoenix Strega converted to Stiletto and the props are all close to the same performance on it with the same header length. If I had more time to fiddle with the header, one of those may shine well above the rest. I saw about a 2000 rpm jump over the stock muffler with a tuned pipe with those props. The 10X10 may not be enough prop for that engine and you may do better to move more air at a lower speed around the fuselage (more diameter & less pitch). I did tach a 10X10 on my 91FX and it did 14,950 on pipe (the pipe was tuned for 13,650 power peak) but I didn't try that prop on the plane.