From what I've read sodium filled valves were first used in air cooled aircraft engines in order to promote heat transfer 'up' the valve stem through the guide and into the heat-sinking fins of the head.
Their use in hopped up flat-heads is a logical progression because the valve is inverted - so the liquid sodium helps to transfer heat 'down' the stem and into very long guides that are in close proximity to the water jackets in the block.
This is very important when one is raising compression ratio - and therefore the combustion chamber temperature . . .
AllPar Web Site Everyone knows that heat rises - so promoting heat to dissipate 'down' a valve stem can only be achieved by improving the thermal conductivity of the material - sodium is outstanding in this regard.
Panic - does the additional weight really matter with a 'valve-in-block' setup? The cam is acting directly on the stem and the additional weight/inertia doesn't need to be offset with spring pressure to prevent float (like it does in an overhead valve arrangement) . . . since gravity is assisting in returning the valve onto the seat.
Gene G. I like what you are doing with this build. I just love hop-ups from this period. I think it is going to be a great cruiser . . .
