Quote:

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...pressure builds up and tries to escape not only through the ring end gaps, but past the rings' seating surface...

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Isn't this exactly what I've been suggesting / asking???

If the only top ring leakage is at the end gap, then there is no reason for the second ring gap to be any larger than the top ring gap (i.e., if the barn's front door only opens wide enough for one cow to go in, the back door only needs to be wide enough for one cow to go out to keep from having a traffic jam ). However, if there is any additional pressure getting past the top ring that isn't accounted for by the size of the end gap (farm analogy continued: a UFO lowers another cow into the barn through a hole in the barn's roof ), then the second gap would need to be wider (but by how much???) to to offset the potential for pressure build-up between the two rings.

BTW, why do we even bother having more than just a top ring with this approach? What benefit does the second ring provide if it's not there to trap the pressure that escapes the top ring? Plenty of motorcycles (2-stroke engines, mostly IIRC) only use one compression ring...