Do piston rings rotate on the piston?

[DMXF]

Originally Posted by olddog

So this begs the question, why not go to the gap-less ring technology, and eliminate the compression ring gaps?

What is wrong with gap-less rings? I never hear any builders say much about them, and as far as I know, I never heard of a new car manufacturer using them (which they may).

I did alot of research on this some time back, speaking with many engine builders, piston manufacturers, etc all the way up to a couple of Cup team engine guys who I was able to wiggle my way into contacting. The big issue with race engines is the weight and while some have run gapless designs at times, they find that a thinner gapped ring provides benefits and they approximate a gapless design anyway through careful gap selection. On a street engine the exact amount of gap closing is variable, so OE conservatively makes the gaps big enough to not bind under any condition. On a race engine, the builders can measure gap closeup in their specific situation and they then make installed gaps just big enough so under race conditions the ring ends are almost touching, ie; the best of both worlds, light weight and gapless performance to within a couple/few HP.

Street performance engines are an ideal scenario for gapless rings, especially with blocks that do not have as rigid of a cylinder wall - the thinner gapless segments conform better to varying cylinder shapes, as well as the gapless benefits are greater at lower rpm where the combustion pressure has more time to work it's way past the gapped rings. Street engines running more miles between oil changes also benefit from oil staying cleaner longer. OE's probably haven't gone that way because the the perceived benefit hasn't outweighed the cost factor (even pennies per part add up quickly).