Heat wrap/ceramic coatings

[QSHIPQ at aol.com]

--
[ Picked text/plain from multipart/alternative ]
For racing, the wrap is probably a good idea, not for underhood temps, but
for performance gains, especially in turbo cars.  The hotter you keep the
exhaust systems, the higher the velocity of the exhaust gasses.  Nascar for example
wraps exhaust all the way to the tip.  Audisport on the other hand, didn't
wrap anything, went for "taper" the length of the exhaust instead (95 S2 rally
car I service is the perfect example - tapered including bends).  Hmm.

The downsides to wrap are the post heat soak problems.  Once you shut down a
hot turbo, all the piping metal close to it becomes part of the cooling
"fins".  If you have wrapped the exhaust, then the heat will get concentrated the
other way, specifically the EM and the head.  Wrap also tends to affect pipe
longevity, longer and more dramatic heat cycling = more metal fatique, cracking
and rotting problems.

WRT coatings on manifolds, I've done them on several customer cars.  I
personally see nothing on the dyno with them or without them, YMMV.  IMO, the reason
is that the exhaust manifold is really short on audi turbo cars, so heat
"loss" really isn't a problem, IOW, the gains from "coatings" are minimal.
Bringing over the left bank exhaust to the turbo on a v8?  Ok wrap and/or coat.

Porsche uses ceramic coating on their turbo cars in the exhaust runners of
the head itself only.  The fact they use it at all, means they could use it
anywhere they felt their was an advantage.  Audisport vented hoods on every turbo
race car I can remember, even the SQ street car.  Sit at a light or shut the
car off and watch the chimney of heat rising from the hood vents, why wrap and
trap?

I gotta say, wrt my urq, the hood vents on the turbo side eliminated my hot
start problems immediately.

HTH and my .02

Scott "no rap" Justusson
QSHIPQ Performance Tuning
'91 v8 (no vents)
'87 t44tqw (vented hood)
'84 RS2URQ project (Dialynx vented SQ hood)
'83 Urq (vented hood)
'87 4Runner turbo (vented hood)


In a message dated 6/7/2003 4:06:36 AM Central Daylight Time, pantg at otenet.gr
writes:

I can also recommend the Thermo-Tec exhaust manifold and exhaust system
wrap.
I have used it on my turbodiesel Land Rover Discovery 200Tdi.
The section I have covered is the exhaust downpipe from the turbocharger to
the part of the exhaust that run the length of the vehicle.

After wrapping this part I can feel the decrease in temperature inside the
vehicle especially when compared with my other Discovery which is exactly
the same type and engine but has not had its exhaust downpipe covered.
As an indication after using the car for a long time you can still touch
(but not hold) your hand on the downpipe, something which is not possible on
the non covered vehicle.

My next projects for the "wrapped" Discovery including wrapping the exhaust
tube up and well after the length of the car where the gearbox and transfer
box. I am sure this will greatly assist into keeping both the gearbox and
transfer boxes cooler and on the same time allow the exhaust gazes to flow
more freely since their temperature is kept inside the exhaust tube and
therefore they should flow more easy.

I have not seen any performance gains but after all on a 3000 kilos 150 bhp
turbodiesel engine (tweaked) it is almost impossible to have any sense of
acceleration (especially when compared with the fast car in the family)

BTW when the RS2 will get its big service (including a precautionary
servicing/check of the turbocharger, timing belt, water pump etc change) I
will try and wrap its exhaust downpipe and tube also.

Take care
Pantelis


----- Original Message -----
From: "Brett Dikeman" <brett at cloud9.net>
To: "Jim Green" <jeg1976 at yahoo.com>; "Quattro list" <quattro at audifans.com>
Cc: <QSHIPQ at aol.com>
Sent: Saturday, June 07, 2003 9:02 AM
Subject: Re: Hood Vents


>At 8:52 AM -0700 6/6/03, Jim Green wrote:
>>I think it's time for some hood vents.  I just about
>>burned my hand when I leaned on my hood yesterday.
>>The area above the turbo is scary hot.
>
>Funny.  My father just solved the heat problem on his 944t.
>
>Header wrap, as per recommendation by John Milledge- widely
>considered one of the 'gods' of 944 engine building.  Sort of looks
>like webbing, and you secure it in place with metal bands that clip
>together.  Installation was aided by the engine being on an engine
>stand :-)  In any case, my father reported a noticeable improvement
>in underhood temperatures post-race.
>
>Milledge specifically said not to coat the inside of the manifold.  I
>couldn't think of why, except endangering the turbo from loosened
>bits of whatever coating you use.  Anyone?
>
>
>Brett