The TOMEI Forged Piston Set 86.00 mm (OEM +1.0) for the Mitsubishi 4G63 uses a high-strength forging process to handle elevated combustion pressure, with thinner wall sections for weight reduction and minimized machining to preserve strength. It features an oval barrel skirt shaped with thermal expansion in mind, a valve recess that supports 1 mm oversized valves, and thinner piston rings to reduce friction loss.