Timing - again, ceramic

[Todd Knighton]

> Yeah, ceramics are a good way to keep the exhaust gases hot and the heads
> and pistons cool. In a book I have called "Air Cooled Motor Engines", the
> author talks about how they tried installing a stainless steel shield in
> the exhaust port to help keep the heads cooler. But, since the exhaust
> gas was now hotter, the exhaust valve ran hotter, too. This can be a real
> problem in air cooled engines. We can expand on this idea and note that
> any technique (including ThermoTec header wrap tape and Jet Hot Coating)
> that "keeps the heat in the pipe" will make the exhaust valves run
> hotter, thus shortening thier life. A solution for this is to get the
> exhaust valves Jet Hot Coated also, and/or use sodium-cooled exhaust
> valves.

	Beware of Ceramics!!!
	Especially on internal engine parts, i.e. pistons, combustion chambers,
valves, exhaust ports.
	In 1989, Porsche decided to put a ceramic insert in the exhaust ports
of the 911's.  Works O.K. on Normally aspirated cars.  When
turbocharged, however, they tend to disentigrate and blow out,
subsequently destroying turbine blades.
	Piston tops coated with ceramic sound great, but on Air-cooled's where
expansion is seemingly twice that of watercooled's, they've been having
a lot of fun trying to keep the stuff on.  Again, on turbocharged
engines, the stuff coming out the exhaust port isn't just going into the
atmosphere.  It destroys things.
	Coating headers as well tends to make the material run much hotter,
thus disintegrates quicker, especially on mild steel.  If you just go to
a good stainless steel header, the coefficient of thermal heat transfer
is so slow, the heat transfer is practically better than a mild steel
header ceramic coated.

Just my thoughts and experiences.

Todd Knighton
Protomotive Engineering