[s-cars] EM and heat question

[CyberPoet]

Scott asked:
So would a high performance coating to exhaust
components which retains heat within the system be
beneficial on our cars?  I also noticed some turbo
hotsides coated on their website photos too.

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All suppositions, but I think the logic will be clear enough to follow:

Q: do they coat both the inside and the outside of the exhaust
plumbing, or only one side?

Internal to the exhaust pathway (increased exhaust temp due to lack of
cooling via transference at the heads/pipes):

- Increased temp to the catalytic converters may cause them to fail
earlier or melt their insides;

- Increased temp to the O2 sensor may cause premature failure or poor
data readings (data that maps incorrectly).

- Increased temp in the exhaust pathway would probably give you lower
hydrocarbon counts, as long as the cats weren't damaged.

- Now, if the inside of the turbo exhaust spool path were coated, I
could see a benefit in terms of reduced heat transference to the intake
side (that makes the most sense in terms of benefit), but heat would
still transfer via the center shaft that connects the two sides. Since
the temp of the exhaust hitting the fins is higher, the bearings for
the turbo would take a bigger beating.

External to the exhaust pathway (decreased ambient temp due to blocking
of heat):

I could see a benefit to the engine compartment components (especially
electrical components -- alternator, etc.). The most major benefit in
the under-hood area (reduced heat to the battery) isn't really
relevant, since the battery is in the passenger rear seat area.
Plastics would have a longer expected life-span (washer reservoir,
etc.).

Total Concept:

I'm somewhat dubious about the whole concept for the exhaust system, as
I suspect a higher thermal non-transient rate would probably be
defeated over 20 minutes or more of driving (since heat keeps getting
added to the system, sooner or later it should reach the same temp on
the outside of the headers/pipes that it would have reached anyway --
the only change being how long it takes to hit that temperature). The
question also arises -- how much of the heat from the cylinder is
usually radiated away from the piston area via heat conductance through
the metal into the exhaust, and if the exhaust's ability to dissipate
heat is reduced, is there a subsequent rise in the combustion area's
metals' temperatures over time? Is it enough to make a difference
(preignition/predetonation, etc).

I could see this as being a great boon for owners of small car engines
who tend to drive for short trips (a mile to the store, a mile back),
but for larger engines and longer driving, it leaves me dubious.

Of dubious advertising merit:

Quoting that various professional high-end race entities use the
coating makes little sense when compared to the general public's
vehicles, since the race teams' engines are designed for very short
usage before rebuild (usually a single race), and heat properties are
different in these engines (heat is dumped much faster via very short
exhausts, they use no catalytic converters).

Just my 2 cents for the weekend.
Cheers
=-= Marc Glasgow
www.cyberpoet.net
Macintosh Help Tampa