stainless steel valves

[Jim Steck]

>perhaps, then, you could explain why going to stainless steel valves
>is an 'upgrade'?  in light of it's poor heat transfer

Durability at temperature . . . strength and corrosion resistance.  The stems
are usually chrome plated or steel stems welded to the stainless steel head.
Conductivity works both ways . . . it doesn't heat up very fast either . . . 

>what might be a reasonable material for an exhaust valve 
>(due to excessive heat)?  yea i know titanium is the 'best' due to
>weight & fatigue factors, but how well does it conduct heat?

My first choice would be silicon nitride . . . very poor conductivity . . . but
no thermal mass.  It makes nice turbine blades for turbochargers (Buick GNX),
and some race engines have used it.  It's even more expensive than titanium, and
less forgiving of shock.  

-Jim Steck