Coats of armour

[QSHIPQ <QSHIPQ@aol.com>]

     Not sure I follow Scott's argument. As I understand, my engine runs a 
     lot hotter during spirited driving and it's this peak heat production 
     that's a concern. Coating the EM helps transfer this heat further 
     along the exhaust system. As you insulate more of the system e.g. 
     turbo hot side and down pipe you can help transfer this heat further 
     from the engine? The exhaust gas speed is maintained (probably higher) 
     because the inside of the manifold and pipes are insulated, and hotter 
     than they would be without the coating.
>>>>  Understand Mike, in a turbo car you WANT the heat in the EM.  The latter
is true only during sustained turbo boost.  Again, you WANT to retain that
heat from those peak runs to help keep the manifold HOT.  A hot manifold all
the time makes for more exhaust velocity all the time.  Peak heat production
in a turbo car in terms of the EM is a plus, not a negative here.

     On shutting off the engine the properties of the coating don't change?
>>>>  The coating will retain heat on shut off (outside coating is what we are
talking about here).  That heat transfer to air with a coated piece of
manifold is less than with a non coated piece of attached medal, say a head or
a turbo housing FI, or a downpipe.  All pieces of medal that don't have the
"sink" properties designed into them like the EM does.  Coating the inside of
the EM moves the heat from the engine.  TO where?  The uncoated turbo (read
heat soak)?  To the uncoated downpipe (read crack that bad boy).  A cast
manifold can absorb a lot of heat and disipate that heat over a long length of
time.  Why mess with those GOOD things by coating the one piece DESIGNED to
address that heat.  The heat you are sending downstream (or upstream on
shutoff) is going to components that have short heat cycles NOT long, stress
cracking defined.
     
 >>>>    I agree that a coated (insulated) manifold will reduce the heatsink 
     effect after shut down BUT the system should be cooler to begin with? 
...  And the GOOD of that is what?  A reduced EM temp does what, it reduces
velocity.  So, do you go after underhood temps, or do you go after maximizing
velocity and leave the coating out of the picture.  I argue the latter, the
former can be addressed other ways.
     
     With a reasonable wind down period it seems like a good idea to me.
>>>  Remember, high heat= high velocity = less turbo surging in the exhaust
manifold.  Look around some Mike, few look at the EM for "gains" in respect to
coating.  Inside coatings are good to reduce heat where you WANT to, I argue
the Exhaust Manifold is EXACTLY where you DON'T want to reduce heat.  Coating
the outside?  Why?  Shut down a hot turbo at night.  Where do you want that
heat to go?  

Plenty of places to address thermal properties in a turbo motor before EM
coating becomes a potential "gain" of any type.  How bout venting some of the
hot air someplace?  How bout putting a heat shield between the IM and the EM?
How bout getting the intake air horn to bring in air that is closer to ambient
and shielding the box from turbo heat?  How bout increasing the size of the
oil cooler?  How bout increasing the efficiency of the turbo?  How bout
coating the piston, valve and exhaust runner FIRST, then look elsewhere.  How
bout coating the EXTERIOR of the IM, FROM heat.  You have a lot of options
before you get ANY benefit from touching a 2 piece turbo exhaust manifold and
turbo with "coating".  

I have yet to see positive performance data on the coating of EM's to be
effective on turbo motors.  Happy to eat that statement for a hot lunch.....

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