Ferrea Exhaust Valve 31.15mm +1mm RB26DETT Skyline Nissan Ferrea Competition Plus Valves have built a reputation as the industry's most reliable extreme duty valve. To manufacture the valves we use special aerospace quality alloys, including the EV8-Z18, which provides high tensile strength. An exclusive two-step slow forging process ensures proper grain flow and virtually eliminates any damage to the material structure. The valves are then heat-treated and stress-relieved over a 48-hour period, which is the crucial base of our molecular integrity. These valves feature avionics-quality hard chrome along with a specially applied hard tip.