ORIGINAL: av8tor1977
While I wouldn't personally set out to build a Ryobi with a "slitted" cylinder, I have to admit that the one my brother has with the slitted cylinder runs well. It turns an 18 x 6 prop at 7700 rpms or so.
I measured the exhaust port width and came up with an approximate dimension of 62% of the cylinder bore. That should be small enough not to cause ring problems if you ground the bridge out of the exhaust port. Does anyone here have experience with doing so? Pinning the ring and then grinding out the bridge in the Homelite 25cc engines helps a lot.
AV8TOR
Leave the bridge attached to the upper port wall, but grind it narrower, and detach it from the lower port wall. Exhaust gas heat will heat the bore side of the remaining lip mor than tha downstream side, so the lip bends away from the piston slightly and guides the ring nicely back into the bore on the upstroke.
Make the exhaust ports wider towards the scavenge (transfer) ports, but only the portion above the transfer ports, so the exhaust port gets a mushroom shape.
If you want to fit a tuned pipe, increase port height by milling the central 1/3rd width port section upwards.