EM 2

[QSHIPQ <QSHIPQ@aol.com>]

S.o.C writes the following (>>) on benefits of coating EM's:
...
>>You bet there is.  There's not a single pro racecar out there running 
>>without it, afterall all an Internal Combustion engine is is a 
>>heat/airpump.  The less heat you waste heating the head and manifold the 
>>more velocity you have at the exhaust outlet, which translate's to more 
>>power.....
>I am a bit skeptical about the benefit of coating the 
>outside of the manifold though ... it would likely help a little bit to 
>keep down the underhood temp, i`but it seems to me it could also lead to 
>heating of the manifold itself ... as the outer insulating coating would 
>prevent the heat from being radiated.  It probably would not be a big 
>deal ... 
>>It's not a problem at all, infact since your transfering less heat into 
>>the metal your making it much harder to warp that manifold. (And if your 
>>running the 2pc EM it's not a problem anyway!)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Normally aspirated cars, the points above apply exactly.  In fact, N/A racers
coat and wrap the exhaust from the head all the way to the tip of the
tailpipe.  This heat transfer doesn't hold sound in a turbo car unfortunately.
The turbine is DRIVEN by exhaust velocity, what happens after it doesn't do
anything for TURBINE performance.  This post implies that putting the heat in
the downpipe/exhaust would "draw" the exhaust gasses thru the turbo, making
more power.  That isn't the case.  You want the highest exhaust heat where you
want the highest velocity.  High exhaust velocity is what drives a turbine.
So you want to heat the EM and the turbo, the higher velocity, the more
effectively the turbine will spin.  More specifically, the higher the
heat/velocity at a lower rpm, the less turbocharger surge you will have
(pulsations in the exhuast at low velocity that make the turbo surge -
referred to on a turbo map as the "surge line").

So coating the exterior of the EM is a good thing for driving the turbo. Turbo
race cars have insulation on both the exterior of the manifold and the
exterior of the turbo, to trap exhaust heat IN those components, increasing
the performance of the car.  At what expense tho?  Trapping heat in headers
and turbos tends to reduce the longevity of those components, fine in a
sponsored race car.  Hardly a plus for those of us that raided the kids
college fund for the 2 piece manifold and HP turbo.  Coating the interior of
the EM on a turbo car pushes the heat downstream, again, moving heat to where
it doesn't help turbo performance, only underhood temps and exhaust velocity
post turbo.  

Really want to give the coating guys business?  Coat the piston, valve, and
exhaust runner, get the heat TO the EM and Turbo.  THAT is what the turbo race
guys do.  That has been done on many a tweeded q as well, a call to Beckius is
all you need to confirm this.  The idea is reduce the heat transfered from
cumbustion in the head.  Ceramics IN the chamber itself allow higher
combustion temps, which allows higher static CR, increasing exhaust velocity
to the turbo, which makes for more power.

Do things for the right reasons.  Plenty of inexpensive ways to address heat
under the hood.  Putting 500USD into coating a 800USD manifold isn't necessary
and B4B, plenty of other places to get measureable benefits.

My .02

Scott Justusson
QSHIPQ@aol.com
'87 5ktqwRS2
'86 5ktqw
'84 Urq