Toa & Arai focuses on research and development considering forging special materials and forms. The samples on this picture have been made with Nimonic and Inconel alloy which are a hard-to-form-material.
Toa & Arai can offer hollow head steel valves than previously. Before 38mm was the largest head diameter but now we can offer the range of sizes from 25.5mm through to 52mm.
The valves are made using a patented forging process from bar stock. The first three steps are hot forging with the last, forming the stem, a cold forging. Currently the process requires an alloy with at least 30% nickel content - meaning that Inconel and Nimonic exhaust valves can be produced - whereas in development is the use of lower nickel content alloy. Titanium hollow head valves are also under development. The valves come with or without sodium filling. This depends on the engine load, whether the valve temperature is critical or weight saving is an issue.