mk e wrote:
My rings are standard tension and the pistons have no gas ports. I asked JE what they recommended and they went with it. I honestly can't imagine gas ports staying open and functional on a street engine....and when they throttle is closed as it often is on street engines they have to be sucking the rings in I'd think. I'm not sure how well low tension rings actually control oil either, again not really an issue on a race engine the basically is never pulling vacuum but it is an issue on the street.
Thinking WAY back I remember that the 308 used to smoke a bit when sitting for longish time in traffic. At the time I used to think it was maybe the mixture was a bit rich to help is idle smoother. I knew the guides were new and tight with new stem seals and the cylinders had been refinished nicely and showed 0 leak-down......so it had to be fuel......but thinking now it was more likely oil getting past the rings and I'm seriously wondering if the gapless 2nd ring wasn't contributing......and perhaps the problem get worse as the gapless ring moves up to the top groove.....like its sucking the rings below it into their grooves and off the wall. Just a guess....but they seal really well......
*LATERAL* gas ports (which are basically radial grooves in the upper surface of the top ring groove help ring seal and work in street engines without coking up.
I'm only ever talking about gapless top rings, as gapless 2nd rings are an abomination before God and Odin.
A gapless ring with pressure on top is pushed down against the bottom surface of the groove. Pressure moves between the ring and the top surface of the groove to get behind the ring and push it out against the bore surface. This seals combustion pressure.
Is a gapless ring with pressure below (intake stroke) even gapless? If the ring is against the top surface of the groove and pressure moves between the bottom of the ring and the bottom of the groove, gas can then flow around the inside edge of the rail and out through the gap in the main ring. This may not as much of a gap as a conventional ring, but they're not gapless on the intake stroke.
Having a gapless top allows the 2nd ring to focus on oil control, which results in better oil control.