BTW this is what 'Hondaman' on the US site says on the one piece rings. He also says his favourite aftermarket rings are MC cycle... oh sh*t I just sold 4 sets of those for 20 quid the lot to get rid as nobody bid on them on eBay:
"The oil ring question: the 1-piece oil rings are expensive to make, for sure. This is the biggest reason the 3-piece type replaced them, according to a retired engineer I met from Perfect Circle in the late 1980s (they used to be REAL big in car engine rings, I haven't rebilt a car engine in a decade, though...). The 3-piece rings have low tension that lets them wear longer IF the bore is properly honed: the machine shop you use must know that, or the difference, which good shops are careful about. I always bring my rings to my guys, as they have 8 different honing techniques and a dozen grits of stones: some of the kits we get today have chrome top rings, some are cast iron, moly, or, in some of my engines, 1-piece oil rings. The 1 piece ring takes a long time to settle in and above 7000 RPM may have trouble routing the oil from the cylinder walls into the oil holes in the ring land (so it can escape from the bore back onto the piston crown area), unless it is CLEAN. This begs the question, of course, of maintenance: if you change your oil like a good boy should, it isn't any grief. If not, the ring can let oil start working past it at high RPM, causing troubles by upsetting the 2nd ring. On the track, this is a killer.
But, on the street, 1-piece has an advantage. The advantage comes in the form of the stiffness of the 1-piece ring: it traps more of the oil under it, wetting the piston skirt slightly better, so improving the heat transfer from the piston to the cylinder. The oil that makes it to the holes in the ring lands then is under quite a bit more pressure, so it keeps those holes flushed out better: I have never seen a clogged oil return hole in a 1-piece oil ring's piston land, but see it often in the 3-piece ring versions. The holes on the latter are marginally closed off by oil debris and need cleaning if being re-used. I have also noticed that the 1-piece oil rings can still rotate on the pistons, but the 3-piece rings NEVER do upon teardown. Thus, I doubt the 3-piece rings rotate, in operation.
The 3-piece rings appear to increase the upper temps of the pistons a little bit, likely due to the lesser oil amounts on the piston skirts. I believe Honda made use of this in the post-K2 engine with the 3-piece rings as part of their 'war' on the "plug fouling problem" in this particular engine (the K0-K1 and early K2 engines (like mine) were famous for sub-1000 mile plug life). In terms of tuning, the K2 with 3-piece rings (post-3/72 production) and the K3 cam, carbs, jetting and spark advancers are all identical, but the K3 did not foul plugs like the K2 always did. Upon teardowns, the K0-K2 (early) has a thickly-coated piston crown (carbon) while the K3 engines show a thinner, light-grey center crust, sometimes even a bare spot in the center. This appears to be from a little more heat, burning off the carbon. The K4-5-6 engines show this in spades.
Another thing I've noticed in engines with the 3-piece rings: by about 20k miles or so, their wristpins are showing measurable wear while the K0-K2 engines with 1-piece oil rings have not only perfect wristpins, but seldom any small-end rod wear. (This doesn't count engines that sat for years, accumulating wetness damage). For years I thought this meant the 1-piece rings were putting MORE oil under the crown to wet those parts, until I went "DUH" one day and realized - the later engine are simply running hotter at the upper reaches of the pistons, hence the extra wear on the pins, too. Sometimes I just feel stupid.."
