As far as I'm concerned I've done all I can with mine.

1) It's a late model with the integral fan shroud
2) Bifurcated transfer ports with substantial radiusing and smoothing of the webs at the entrance to the ports (see posts 134 and 145). Unfortunately I don't have a measurement of the effect of the T port mods.
3) Two ring piston and "I" beam style rod. This only means that the stock rings on the later Ryobi seal just fine and the rod may be stronger than the older Ryobis.
4) Contoured reed valve to precisely match seat.
5) Bent reed clamp so the reed clamps at just the base of reed as opposed to stock which clamps well down the reed toward the port opening. This gives less reed force required to open.
6) Enlarged cylinder exhaust port to give increase port area and 160 deg timing.
7) Stock muffler with 5/8" ID outlet pipe replacing the 1/2" ID stock internal pipe.
8) 12.7 mm venturi carb.

It is my belief that the major performance producing mods are, at least for the late model motors, in order of importance:

1) Larger exhaust pipe on stock muffler or after market exhaust.
2) Larger carburetor
3) Exhaust porting

It is my intention to eventually get a performance derivative on the transfer port entrance mods to see if it's worth doing. It's a fairly time consuming process.

I would also like to work up, from stock, one of the older Ryobis. I'm collecting parts now but am still lacking a good cylinder with the single runner transfer ports. I also don't have a stock muffler anymore as I modified the extra one I had it to see if opening it way up would make any improvements.

My Ryobi is developing 15 lbs. of thurst at sea level static conditions with an 18 x 8W APC prop.

Most of these mods are explained in detail somewhere in this thread.

Also see post 332 where combatpilot is getting 14.2 lbs thrust with an older style Ryobi AND a different prop. From reading some of the discussion information available I get the notion that APC props are the most efficient ones out there so it's possible that combat's motor may give more thrust with the APC prop. For the older Ryobis, as combatpilot and others stress, you must first be sure the piston ring is sealing well for good performance.

diceco