Now that I gave it a little thought, is there any reason a person couldn’t get a slight over bore size piston and lap it into a perfect fit?
Rings are a gas check of convenience. Easy to fit, easy to replace. Allows “sloppy” piston fit and mismatched thermal expansion to keep manufacturing cost low.
But you dont need them.
A perfect piston and bore would be one that the piston swells perfectly into the cylinder at op temp. Full contact would allow much better heat dissipation.
Frow in a couple em oil retaining dimples.
Surely this isn’t so labor intensive that nobody has ever tried it. Exhaust port could be almost 360* and the ringless piston wouldn’t care.
I know it is much easier on a 25cc engine. But if the model airplane engines have them and run 20K+rpm, it could be worth a try.