<VV> FW: Ceramic Coatings Questions (Kevin Nash)

[Brandes, Guy]

More ceramic coatings stuff to pass along.
 
Regards,
 
Guy Brandes
 
65 VAIR  140

Subject: RE: <VV> Ceramic Coatings Questions (Kevin Nash)
 
Hi Guy,
 
Having been interested in turbos over the years, I had been very
interested in how ceramics affect turbo performance.  I asked John at
Lo-Ko about the situation.  
 
He replied that I SHOULD NOT coat the turbine blades- the coating was
too thick, and there would be no effective way to assure proper balance.
Coating the internal heat shield (the round cast iron piece behind the
turbine blades) might reduce transfer of heat to the oil and bearing,
but he wasn't sure of the clearance (the coating is several hundredths
thick).  
 
He thought that coating the combustion chamber would have a similar
effect on octane requirements as normally aspirated motors, but he
hadn't done a turbo.  Reading the comments below gives us actual field
experience.  
 
Coating the exhaust port, exhaust stacks (tubes), and manifolds (logs)
will definitely help in two ways: reducing heat soak into the heads, and
retaining heat energy in the exhaust stream, which will enable the turbo
to spool up faster.
I would coat the inside and outside of the exhaust pipes from the
manifolds (crossover and riser) both for heat retention and to reduce
corrosion, as the increased heat will erode the steel pipes.  Caution
should be taken, however, not to coat the portions of the pipes which
slide into one another- clearance will be a problem.
 
Downstream of the turbo unit is a non-concern; the heat energy has been
used, and the quicker you get rid of the waste heat, the better.  You
might consider coating the pipe from the turbo to the muffler for
cosmetics and corrosion resistance, but trying to coat the muffler is a
waste of time and money- there is no way to coat the muffler's interior.
 
I have no idea what the increased heat will do to a muffler- it is far
enough downstream that it may not affect its longevity- the quicker
warmup (and subsequent drying of acidic condensation in the muffler) may
actually help, but that's just guesswork on my part.  I have noticed
that on almost all Corvair mufflers, the first place it rusts is where
the muffler strap goes around the muffler body.  This is due to
electrolysis from the (slightly) different alloys used, combined with
the heat.

I might note that I have been told that coating the manifolds alone will
lower the head temps significantly, regardless if the head internals
have been done.  From my own experiences, I can tell you that warmup
time for my wife's engine seems no longer than the uncoated 140 in my
Corsa- properly adjusted damper doors and thermostats are the key,
there, and total output from the forced air heater appears to be
adequate, even though I have yet to install a high-speed blower
(besides, how likely am I to use the heater much in a '69 Convert in
Chicago in the winter?)
 
Piston expansion is not much of a concern- really, as far as combustion
goes, the piston is just a way to fill the big hole in the compression
rings- those are what actually contact the cylinder walls.  BTW, I did
have the piston skirts coated, not with a heat reflective ceramic, but a
low friction substance.  
 
Coating the piston crown protects the piston from temps that approach
the melting point of aluminum, keeps the surface of the combustion
chamber cool (the top of the piston is to be considered part of the
combustion chamber surface area), and reduces heat transfer to the
engine oil (which, after all, is the main way the pistons get cooled).
 
Note to Kevin:  Did you try thicker head gaskets, or perhaps stacking
extra barrel gaskets under the cylinders to lower the compression? 
 
Kirk