<VV> VirtualVairs Digest, Vol 45, Issue 86

[kevin nash]

> ------------------------------> > Message: 2> Date: Tue, 28 Oct 2008 06:58:50 -0500> From: "Brandes, Guy" <GBrandes at loebermotors.com>> Subject: <VV> FW: Ceramic Coatings Questions (Kevin Nash)> To: <virtualvairs at corvair.org>> Message-ID:> <420198DE0F8CAD40A63CD2D3E5FBB6A6021DFC23 at LIN-LOEBER01.internal.loebermotors.com>> > Content-Type: text/plain; charset="us-ascii"> > > 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 > > > > > ------------------------------> Kirk- Unfortunately, I had the heads off to drop the compression, only to find out that the head gasket surface was buggered up in some places, and was likely caused by too many pinging/detonation events. The gasket surface needed to be repaired, meaning that they had to take .010" off, and that also
meant that the combustion chambers needed to have their coatings stripped and then re-applied, or just stripped. We ended
up stripping the coating and did not re-apply. My big mistake
was thinking that the effective compression ratio rise was going
to work the same in the turbo as it would in a n/a application,
and that i would only have to back the timing off. I thought that
any "out of boost" pinging issues that my friend was experiancing
wouldnt apply to my to my application because I was running 
early turbo heads and not late turbo heads, the late heads
supposedly being more ping prone than the early ones. Maybe
they are, but I wasnt able to see any extra ping resistance.
I honestly believe that if we had set the static compression
at say, 7.4, then the thermal barriers would have worked as
though the engine was at 8.0 or 8.2 to one, and then i wouldnt
have had any problems.
Kevin Nash
efi 63 spyder 
 
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