Chainsaw Repair

The case of the 372xp is stronger, and a bit heavier.

The one vs. two ring piston has to do with the EPA version of the 372, and not really with the 371 vs. 372.

I suspect the two ring pistions was a US/EPA thing mostly. 

ya but pretty near all these size saws come with 2 rings , first time I seen a 2 ring piston up here was in the cut-off saws

In your opinion, what is better? 1 ring or two? For work purposes.

I had a 372 50mm wood port by Dave Neiger that only had the top ring on the epa 2 ring piston. Also had a woods ported 372 with 375K cylinder I think it had both rings on it. Cant remember on that one, but pretty sure it had both rings.
These were woods ported work saws / GTG cookie cutter saws. Still could be used for work doing firewood etc.

My thinking was less drag on the 1 ring.

One piston ring use for racing is nothing new.
Here is a picture of my older brother Cliff making 3 cuts in a 12"X12" white spruce [cold start] at a good old competiton at Cranberry Portage, Manitoba's winter festival. Feb. 1976
He cleaned up with a 1st place finish for years with that Jonsered 80 and only when he retired it in the early 1980s did he tell us his secret was pulling the bottom ring.
But his saw handling skill was also #1. Not once did he ever get disqualified for cutting into the lines spaced 2" apart all around the cant/log. Look close in the picture and you can see the lines marked on the log, an idea that came from Quebec in the late 1960s.