[Excaliber]

Seems to me sodium filled valves used to be fairly common 'back in the day' and widely available for lot's of different motors. You don't hear much about them today except for things like 'they break'. I don't know if thats really the case or the valves are just getting a bum rap.

Steve, I checked that link, sure enough it says sodium filled exhaust valves on the new Vette.