I do, and I do.

100 octane valves have a different seat angle and a smaller stem diameter
than 80 octane valves.

Lead is the big problem with 100 octane in a low compression engine. While
the gasoline itself and the combustion process makes not a whit of
difference in the temperature of combustion, the compression ratio does.
Gasoline in a high compression engine burns hotter, be it 80 or 100 octane.
Tetraethyl lead requires a relatively high temperature to be completely
vaporized and exhausted in the combustion process. A high compression
engine does this, while a low compression engine does not. Bromine is
introduced to the mixture in an attempt to "help" the lead "burn", but even
bromine doesn't do much in a low temperature environment.

The different seat angle is an attempt to "get the lead out" of unburned
tetraethyl lead. Even so, the low temperatures encountered in a low
compression engine lets the lead coagulate on the first cool surface it
finds. That happens to be the valve stem. Therefore, the valve stems are
ever so slightly reduced (.005" comes to mind) so that the lead can plate
out on the valve stem and still not cause the stem to stick on the guide so
often. "So often" is the operative term here. 100 octane will cause valve
sticking, but with the 100 octane valves, just not quite as soon.

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford

"Scott" wrote in message
.. .

Like I said, MIGHT OK, if there is no difference in heat, what are the
100 octane valves in my A-65 for? Or more generally, why do they sell 100
octane valves for A-65s and C-85s, etc. that were certified on 80
octane??? Like I said, I use them, I don't wrench on 'em

Scott