[s-cars] EM and heat question

[serge]

on 7/11/03 3:49 PM, CyberPoet at thecyberpoet at cyberpoet.net wrote:

> 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.
>
> ------
> 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
>
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>
Marc,

According to the fine folks at Jet-Hot

http://www.jet-hot.com/pages/techinfo2.html

"JET-HOT increases the endurance limit (fatigue strength) of most alloys
subjected to stress loads, such as vibration produced by an engine, after
exposure to high temperatures. In addition, JET-HOT does not contribute to
hydrogen embrittlement, a condition associated with chrome and other
coatings in which microscopic cracking can lead to premature and sudden part
failure. The comparison to the left represents the average performance of
403 stainless steel, uncoated and coated with JET-HOT, after 10-million
stress cycles. The results demonstrate how effectively JET-HOT protects
substrates from thermal fatigue. "

They have a nice little chart too.

My understanding of the benefits of internal/external coatings:
corrosion/fatigue protection, faster exhaust gas velocities, some level of
underhood heat containment (even for extended high rpm stints).

I am no expert, but I was under the impression that catalytic converters are
the hottest part of your exhaust system due to the chemical exchange that
happens within, and that the hotter the exhaust temp. the better.

I was sold on the Jet-Hot product, and had my RS2 EM and Stromung downpipe
coated. I went with the their Jet-Hot 2000 product in gray (not all that
attractive, but has a higher temp range). I have had the parts on the car
about 3 months (one track outing), so far the parts look the same as when
they were installed, dull gray. I will keep an eye on said items and post
any issues if they develop. So far I am happy w/ the product, seems to work
as advertised. I only wish I had taken some temp readings for before/after
comparison. My old EM and turbo housing used to glow cherry red, the new set
up does not, wish I had some numbers to back that up, but no such luck.

In dealing w/ Jet-Hot, THEY WILL COAT EVERYTHING YOU SEND THEM INSIDE & OUT.
I had specific instructions about which surfaces I wanted coated and which
ones I did not wish to have coated. They promptly filed my instructions in
the circular file and coated everything inside and out. This did not turn
out to be a problem, but as far as them following specific instructions,
forget it.


Serge Filanovsky

95 S6 Avant