[email protected] (Dave Williams)
fordnatics  30 Mar 1995
- -> was interesting to me was "why". The article said that the sodium ate
  -> away at the inside of the valve and, with time, weakened it.
- First I've ever heard of it.  There's a gazillion VW Transporters still
  running out there with sodium filled exhaust valves, not to mention
  Diesel trucks, aircraft, marine engines, and whatnot.
- VW Transporter at idle:  "putt, putt, putt..."
  VW Transporter at redline:  "putt, putt, putt..."
  not exactly a high performance application, but they spend most of
  their life with the pedal to the floor.
- The sodium filled valves are expensive.  The stems are thicker, which
  doesn't help flow a lot.  Finally, you have to really, really abuse the
  engine to get into the territory where sodium filled valves start to
  make sense.

[email protected] (Dave Williams)
fords  01 Apr 1995
- -> Well, sodium filled valves have a hollow stem, and they are two piece
  -> valves with the head fused to the stem after the stem is filled with
- FYI, I've never come across a sodium filled valve like that.  All the
  ones I know of are one piece forgings, drilled down the stem, with the
  ends plugged by a welded or swaged tip.
- Holman-Moody used sodium filled valves in their NASCAR big blocks, and
  also for the GT40s they built for Le Mans.  Did pretty well at both, as
  I recall.
- -> The life expectancy varies, but in all circumstances you can be
  -> assured they will fail.  When used in a race car, you are lucky if
  -> you finish the race.
- Aw, come on, Dan.  Sodium filled valves are just another solution to a
  problem.  You can misapply anything if you try hard enough.  Most of the
  valves are designed for low to intermediate RPM operation; drop them in
  a 10,000+ RPM drag motor and you'll probably wind up with rubble.  Stick
  them in a road racer in a 24 hour endurance race and they'll last just
  fine, thank you.
- -> The purpose of the sodium filled valve was to keep the exhaust heat
  -> in the head of the valve and not let it move up the stem.  If the
  -> heat was allowed up the stem, it caused the valves to seize in the
  -> cast iron guides
- Uh, no.  The idea is to help transfer heat up the stem, into the water
  jacket, to cool the head of the valve.  Early valves used plain old NaCl
  (table salt), later ones used metallic sodium.  At operating temperature
  the sodium would melt and be shaken up and down the stem with valve
  action.  The moving sodium slug and thinwall stem transfer heat better
  than a solid steel stem.