Date:         Thu, 23 May 1996 08:35:34 -0400 (EDT)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Dirk Wright <wright@uspto.gov>
Subject:      Re: The transitional engine...

On Wed, 22 May 1996 vwbus@tcpbbs.com wrote:
> 
> But onto aluminum, you know he might have something here, how about
> hardcoat, ie thick hard anodize.  In the world of rocket science about
> here every bit of aluminum subjected to wear or intended to resist
> corrosion
> recieves such treatment.  I'd bet under $100 a head and might make em
> last forever.  Also makes em non-conductive on the surface, ie should
> not corrode?

I looked into this a little and I concluded that anodizing was not a good
idea for VW heads. First, the main mode of heat removal in this situation
is conduction and convection (radiation is least important).  Heat is
absorbed in the combustion chamber and exhaust port by all three modes.
Anodizing is conversion of the top layer of aluminum into a tough, and
hard ceramic-like material. This layer has much less thermal conductivity
than the raw aluminum, so in the portion of the head exposed to combustion
heat, less wold be absorbed, but less heat would also be removed by the
cooling air on the outside of the head. Further, anodizing greatly
increases the coeffieicent of abosrption due to radiation, so more heat
would be absorbed by this mode in the combustion chamber, and more would
be radiated on the outside. Finally, the anodized surface is brittle, so
it would crack due to the extreme temperture changes that occur from
startup to operating temperature, and from the compression in the 
cylinders. Another hassle with anodizing is that the head has to be 
stripped of all non-aluminum parts before it can be anodized. any foreign 
metal in contact with the aluminum will interfere with the chemical 
process and basically ruin it. this means the seats, guides and studs 
will have to be removed. the problem is when you go to press-fit them 
back into the now-anodized head, the anodized surface wil crack, thus 
ruining what you set out to do in the first place.

The best idea that I've come up with is Jet Hot Coating for the
combustion chamber, intake and exhaust ports and exhaust valves only.  It
would cost about 1-200$ per head, and I haven't called them to get the
details. Jet Hot is a metal-ceramic coating that can be applied to 
spcific areas and has been race and aircraft proven for years. It is a 
thermally insulating coating of extreme toughness. The coating bonds with 
the metal and requires a 3 step treatment. Another area that would be 
good to get done are the piston tops. The idea is to insulate the head 
and pistons from the heat of combustion, thus reducing thier temperatures 
and extending thier useful life.


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Dirk Wright 						       wright@uspto.gov
"I speak for myself and not my employer"                   1974 Porsche 914 2.0
"A real hifi glows in the dark and has horns"
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