Re: RE: Whats the sodium for?

["Smith, Kirby A" <kirby.a.smith@lmco.com>]

Glen's thread continues:
________________________-
I don't think the OEM valves on NA Audis are SS (Stainless Steel).
(but then I was wrong about the sodium-filled valves!)

- -glen

>For severe-duty turbo service, are the sodium-filled valves better or are
SS valves better?

Audi used sodium-filled valves on turbocharged engines and solid ones on
N/A engines. I guess this answers the question.
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There is an aspect of apples vs. oranges here.  Valve longevity is aided by
both cooling and temperature resistance.  Given a metal with sufficient
ductility, hardness, whatever for valve use, then higher temperature
resistance is better.  This is generally associated with high nickel content
(SS, Nimonic 80A, ...)  

For better cooling, sodium can be used to transfer heat from the valve head
to the stem, where the oil splashing about can cool it.  It was my
understanding that sodium-filled valves were only partly filled, so the
sodium was cycled from head to stem as the valve moved up and down (or vice
versa).

                .... Kirby   (Kirby A. Smith)
                              2 x 1988 90q
                          New Hampshire USA