Thread: Piston ring question

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Hypers run hotter on the top ring, so need additional end gap to prevent butting. You are correct, 0.026"/0.027" on the top ring for a 4" bore. The second ring can be gapped conventionally at 0.0045" per inch of bore (0.018" for a 4" bore).

The first and second rings have a chamfer on the top inside corner. This chamfer on the top ring goes up when installing the rings. Upon combustion, the pressure comes down the side of the piston, then travels between the top of the ring and the top of the ring land, pressing the ring down on the bottom of the ring land to form a seal. It then travels to the back side of the ring to compress the ring out against the cylinder bore and contain combustion pressure. The chamfer on the ring edge allows the gas to make the turn from the top of the ring to the inside edge of the ring. The second ring is the scraper ring and the chamfer goes to the bottom of the ring.