Sodium and Silicone and Torsen

["Janet Scruggs" <scruggs@mbay.net>]

Dearest group,  Some recent questions and comments have spurred me to
respond.  Sodium in exhaust valves has been around for a while.  My '67
Rover 2000TC uses them and while it doesn't see the heat of a turbo engine
it is a one hp per cu in, two liter engine with 10:1 CR.  As a side note,
even sodium cannot protect your exhaust valves from burning when you run an
engine designed for 100 octane leaded gas on 93 octane unleaded gas. (Do
not be so rude as to ask me how I know this.)  I understand the lead
deposits coat the valve stems to form a rather tight 'running fit' between
the stem and valve guide which further promotes heat transfer from the
valve to the head.  

In same said Rover I have used silicon brake fluid for years, starting in
'76 as it first came available from Dow Corning, without a flush or second
thought.  Have not experienced any hydraulic failures using it either...
for a Rover this _is_  significant.  From my experience, it is compatible
with DOT 4.  I think this has been said recently, but my understanding of
why silicone fluid is incompatible with high performance brakes is thus. 
Unmodified liquid silicon is a rather high viscosity fluid and therefore
near impossible to fit into a hydraulic system.  It is mixed with a
viscosity improver, no idea what, to achieve acceptable liquid states. 
Upon heating it is the viscosity improver that boils locally and expands so
that when the pedal is pressed you are now compressing a gas rather than
transferring pressure to the pistons.  So, don't use it in your high
performance car, or the SUV being pushed down a long winding hill by a
large trailer, as it will "fade."  But for Al's Fiat, or mom's minivan,
things that are only driven rarely or lightly... it is good stuff.

Regarding the inventor of the Torsen... the engineer referenced in the
recent "low tide in the gene pool" anti-Audi rant was probably the one who
did the integration for Audi, but not the inventor.  It was invented by a
mechanical engineer named Thorsen, who I think lived in the northeast US. 
Had he not sold the patent to Gleason Gear (Co? Inc?) the thing would now
be known as it originally was... the Thorsen Torsen.  

Regards, Gross Scruggs