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Keith Black hypereutectic pistons place the top ring close to the top of the piston, which subjects the ring to greater heat, demanding a larger top ring endgap of 0.0065 inch per inch of bore. A 4.155-inch bore puts the top ring gap at exactly 0.27 inch. The 0.030-over 5/64-inch Federal-Mogul rings measured 0.18 inch, so we had to open the gap with our handy electric ring grinder. This is a critical step. If the top ring gap is too tight, the ring will stick and break the piston. We've seen it happen.