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Only one post out of the batcave and....

Be careful with coatings folks, you may or may NOT be getting the gains you
may think.  "Fast and faster" q claims are always just that, some data again
may be more appropriate.  I could argue that coating on the manifold either
inside or out does little for performance.   Not sure I understand "both" at

On coating the inside:
Coating the inside will move the heat downstream while the car is running.
Well, assuming you didn't coat the turbo, then the heat will be more
concentrated there, increasing the risk of turbo heat soak, certainly a
problem when the car is shut down.  If you did coat the turbo, then you shoved
it further downstream to the downpipe, defeating the whole idea of exhaust
velocity increase = turbocharger performance increase.  Since exhaust velocity
INCREASES with heat, then the velocity = heat IN the manifold should be the
highest to avoid turbo surge, not sure I understand why you'd want to move it
downstream.  The third issue is carbon buildup:  Take the EM apart after a
couple weeks of turbo blasting, what do you find?  Carbon buildup on the
coating (btdt).  So the "smooth" flow benefits aren't there either....  Ok,
now let's go to the outside

On coating the outside of the EM:
Given the choice, this has better velocity characteristics, at the expense of
a potentially more problematic heat cracking issue.  Since you are trapping
the heat inside the EM, exhaust velocity will be higher (for a given
manifold), fine while the car is running.  What happens on shutdown.  Well,
any insulator you put on the manifold now becomes an insulator from heat
exchange to cooling air.  What property happens now?  Well, the fastest place
for this heat to go is to the aluminum head.  The next place this will
propogate is in the turbine housing, neither of which seems all that appealing
to me.  Bottom line,  you might very well be going backwards in practice from
the very reason the 2 piece manifold was introduced in the first place

Managing thermal loads is what turbocharging is all about.  Understanding what
you are doing, and the difference in what you are doing car on vs off, is just
as key here.  A MEASURE of performance gain pre and post coating might be
convincing, though not sure even necessary.  Coating TO the exhaust manifold
is sound in practice and theory, i.e. pistons, valves, port runners.  Coating
a manifold and turbo might be "cool" under your hat, but it could also head
you down the wrong road for the wrong reasons, btdt.

Many have tried to convince both ways on the practice and theory of coating
the exhaust manifold/turbos.  No hard data ever attached.  Moving heat TO the
EM is good and sound, moving it FROM the manifold, doesn't help velocity =
turbo performance, only underhood temps.  Two completely different reasons
with two different thermal goals associated with them, the latter hampering
the former.  Plenty of other places to spend time and $  on, with measureable
performance gains, than the EM, coating or no.  Get the 2 piece an bolt'er on.

Coatings?  Not sure, don't do it.  Heat soaking an exhaust manifold is NOT a
bad thing folks. Put a 10 dollar shield between the EM and IM, and be done
with it.  Doing it?  Best make sure all your post shutdown cooling systems are
fully operational.


Scott Justusson
'87 5ktqwRS2
'86 5ktqw
'84 Urq