RE: Whats the sodium for?

["Douglas Hurst Quebbeman" <dougq@iglou.com>]

> > >In the turbo head the valves have sodium in 'em.  How does this allow
> > >you to run more boost?  Does it cool the valve better???
> > 
> > As the valve opens and closes the liquid sodium moves inside the valve,
> > taking the heat away from the tip and transfering it to the well cooled
> > stem. Liquid sodium is an excellent heat conductor - it is used on some
> > nuclear sumbarines for cooling reactors.
> > 
> I'm not sure that sodium reaches a liquid state at the temperatures
> encountered in even a turbo-charged internal combustion engine. Anyone got
> another theory?

Sodium melts at 97.8 deg. C (208 deg F). So yes, I'd
say it's definitely melting. So simple convective 
cooling is taking place. Once the sodium has melted,
the hotter sodium rises up away from the valve face,
carrying the heat to the valve stem, where it's then
conducted out by the rest of the valve train. Then, as
the sodium cools, it falls back down the valve stem
toward the valve face, where all the heat is being
generated.

Very nice system, and I was surprised the first time
I heard about it (this was before I understood what
Vorsprung Durch Technik means).
--
-Douglas Hurst Quebbeman (dougq@iglou.com)            [Call me "Doug"]
    QuattroClub USA# 4536              Audi International # 100024
       74 100LS Auto, 77 100LS Auto, 84 Coupe GT, 86 5Kcstq   
"The large print giveth, and the small print taketh away."  -Tom Waits