[Woodz428]

They were used for many years on VW van engines, I still have several new ones left over. My understanding regarding the 427 valves was that they would pop the head if they weren't warmed up to temp prior to hammering them. The sodium turns to liquid under heat and the sloshing aided in cooling of the head. I never used them because of the extra expense and the spotty record. The ones in the VWs never encountered a problem like that, although VW valves in general will pop heads after extended use in an engine from stem heat fatigue crystalizing the grain structure. I think the lightweight, head diameter in relation to the stem, plus lower revs made them less of a problem than the 427s were.