Pitch can make a pretty big difference on static rpms. This is because when a higher pitch prop is not moving through the air, a good portion of the blade is stalled and causing a ton of drag. This is also why lower pitch props are used for 3D flying, as lower pitches are more efficient at lower, or zero, airspeeds. As an aside, this is also why high performance full size airplanes use variable pitch props.

I keep telling you guys, a Frank Bowman ring is the first mod to do after you have a free flowing muffler and an 11mm carb on a Ryobi. The second thing to do is raise the exhaust timing to 150 degrees.

Take a good used cylinder, sand it carefully with 400 to 600 grit sandpaper, and put a Frank Bowman ring in it. If your engine isn't sealing well, all the mods in the world won't help as they should. It is just basic good hot rod practice to overhaul a used engine before modifying it. Bearings, seals, and ring should be perfect first, then start modifying. An aftermarket muffler costs 30 to 40 bucks, a carb retails for around 40 bucks, an ignition system is 80 bucks plus, a lowly prop is at least 15 bucks. A Bowman ring at $12.00 shipped is a cheap investment, and they flat work.....

Once again, I have many times seen engines with moderately worn stock rings gain 600 to 800 rpms with a Bowman ring. The recommended ring gap for engines of these sizes is around .003", and I'm betting all of yours are significantly more than that.

AV8TOR