Valve specifications with the largest hollow area possible while still assuring the strength of welded areas were established, achieving a weight reduction of 4.4 g per valve, and applied to races. In addition, a high-quality oxidation resistant process was established for filling titanium valves with sodium-potassium, and technology that cools the high temperature areas of the valve by 100°C or more was developed. These cooling effects enabled expansion of the hollow area, further reducing the weight by 4.8 g per intake valve and 4.6 g per exhaust valve. Engine 2-race event durability tests were completed, but the intake valve experienced a drop in output due to the effects of sodium-potassium heat exchange, and some issues with exhaust valve durability also remained.
Article of Honda R&D Technical Review F1 Special (The third Era Activities) (257 - 259)