Just bumping this old thread on the pro's and con's of one or two ring setups for saws. The single thin ring has some definite advantages for an all out race saw. The limitations there and the operating conditions and clearances are a totally different set of conditions than a working saw. Port size in relation to piston diameter and ring bulge into exhaust port have some different implications than on a stock saw.
Heat transfer out of the piston crown is probably more effected there by evaporative cooling than ring conduction. Crown diameters have to be given more clearance. Above about 10 thousand rpm it probably would not be noticeable to the operation whether there was a ring or not. It is quite common to use only one ring of a two ring piston, perhaps because of the negative effects of pressure trapped between rings reducing an upper rings stability at threshold piston speeds.
Rather than thousands of hours at much much lower mean effective pressures of a work saw, a typical run might be 5 seconds at full output. A little more on some of the West coast big wood competitions.
As gypo mentioned unburned charge in the ring grooves and between rings have been considered in regard to meeting EPA requirements. It does seem that more saws are going to the two ring set ups but I bet there are a lot of factors involved and not a simple explanation of why. I did see discussed on another forum by an operator who puts high hours on saws limbing small diameter pulp and his experience with one and two ring replacement time on the same cc class saws doing the same work, was not clearly decisive one way or the other. I may just dig him up and ask if his opinion has changed. I know he has run the older huskies, stihls, the 346 huskies and the 5100 dolomars.
Just throwing this in to muddy the waters on the topic, Lol!
