The function of which valve sheet is asked, is maintaining air tightness with a valve, and generally wear resistance is required. However, with the engine used by high rotation and high load, the cooling performance of a valve sheet becomes very important further, and it is greatly concerned with an engine output.
When engine is high rotation and high load, it is impossible to achieve high output from the engine if cooling performance of the cylinder is low and knock limit does not become high, since the temperature of the circumference of a cylinder head rises unusually. In racing engines that temperature needed to be carefully controlled, how much you can cool the circumference of the sheet ring is the important issue, and the technique of using high heat conduction metal, such as copper for a sheet ring, has been taken.
Copper has one of the highest thermal conductivities through all metal that enables receiving heat from cylinder and cool it down quickly by transmit the heat to the cylinder head. (Degree of heat conduction: 1.silver, 2.copper, 3.gold, 4.aluminium, ... 10. cast iron - STD). Tomei select beryllium copper alloy (BeCu) that can secure mechanical intensity most in the copper alloy, which has ideal fatigue resistance and wear resistance while securing a preeminent cylinder cooling performance. Tomei named it "bery-ring" and applied it to the high performance turbo charged engine.