Originally Posted by skunk2 website

Skunk2 Racing valves are made from SAE EV8 stainless one-piece forgings, which are then heat-treated using a proprietary heat treatment process. After CNC-machining and swirl polishing, a PVD black nitride coating is applied to reduce friction and increase wear resistance. Skunk2 Racing valves are lightweight, durable, and offer excellent heat and corrosion resistance. Skunk2 Racing valves are available in standard and high compression styles and also in various sizes. Oversized valves should not be used with standard size valve seats or with Stage II and III VTEC camshafts.