FW: [s-cars] EM and heat question
Trevor Frank
tfrank at symyx.com
Mon Jul 14 11:49:41 EDT 2003
-----Original Message-----
From: Trevor Frank
Sent: Monday, July 14, 2003 10:49 AM
To: 'serge'
Subject: RE: [s-cars] EM and heat question
Interesting, but if it is coated only on the outside the temp of the
header would increase, decreasing the strength, most likely and cause
more problems. If it is only coated on the inside then I could see a
benefit to the material itself, as long as it doesn't flake off and
damage the turbo or cause localized heating and warp or fracture the em.
I like the idea of keeping all of the heat in the header before the
turbo, and keeping all of the heat as it goes through the exhaust side.
Heat~energy~velocity. On the down pipe though, unless you are trying to
either protect a crappy metal, like 10X0 or 304ss from failing by
coating the inside or keep under hood temps down. A coated down pipe,
hek a coated header will act in similar fashion to reducing the tubing
size. This is because you keep the heat in and therefore increase the
velocity witch increases the back pressure.
I have used coatings from Jet Hot and HPC on all of the mild steel
headers that we have put on race cars. I have never seen a benefit from
the dyno. I have never had one that didn't eventually flake off. I
have had to have them recoated about every 5-8 years.
-----Original Message-----
From: serge [mailto:serge411 at speakeasy.org]
Sent: Saturday, July 12, 2003 3:27 PM
To: CyberPoet; otw185 at yahoo.com
Cc: s-car-list at audifans.com
Subject: Re: [s-cars] EM and heat question
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
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