Re: Whats the sodium for?

[James Marriott <marriott@micron.net>]

Haudi,

quattro wrote:
> 
> So, the way I read this is that Audi used sodium-filled valves on the turbo cars because the standard
> valves were not up to the job and SS must have been too expensive for production use?
> 
> -glen

I doubt that the cost issue prevented the use of SS. SS is about 10%
_less_ thermally conductive than regular carbon steel. If _that_ has
heat trouble, the SS surely will.

cu
James
'87 4kq, plain valves
'89 200q, sodium and K26
'64 Falcon, plain valves, 16 hardened seats

> 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