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We need to understand what is happening in the relationship between Steel headers and the coatings in the microscopic level. I will try to explain as simply I my limited skills will allow.
Steel expands with heat. The rate of expantion is directly proportional to tempture. That means that near the head is hotter than at the collector and therefore the metal is expanding more at the head than at the collector.
If the coating is harder( I use harder for lack of a better word but like ceramic) than the steel, then what happens is it fractures as the steel expands, leaving microscopic cracks in the coating which allows moisture to get in and you know the rest.
Asking any coating to go through that kind of thermal expantion and be able to match the exact rate of the steel is a very tall order. Now I'am not a chemist, but I have worked with metals in industral applications and can say this, even the big boys accept this fact and just try to keep it painted or let it rust and replace it when it is no longer servicable. I only posted this to help you think about things before you spend the hard earned bucks for fancy stuff that can only delay the enivtable. I mean I can buy 2-3 sets of plain ole headers for the price of the fancy ones that the coating won't help the usual speed bump dents and other damage that headers usually endure.


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Harley
69 461 El Camino Nitrous Model
69 Chevelle coupe
71 SS Camaro
75 L-82 Corvette
71 Gremlin X
Kerrville,Tx.
 

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Mine were coated by a company called HPC, High Performance Coatings, in Salt Lake City. They are fine six years later.

I can't remember the thickness of the coatings, but it is really thin. I had my mountain bike frame coated, and the extra material didn't even register on a pretty good scale. Maybe it's so thin that on headers, it can expand and contract along with the steel. Since I have had no problem, I haven't even given it a thought. I would do my headers again.
 

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Your theory is correct but I've had the JetHot's on my car for 3 years and they look like new. They must be doing something right because they warranty them for life against rust throughs.
 

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The "ceramics" used to coat headers is probably pretty high tech stuff. There are different types of ceramics. Crystalline ceramics is what is used to make those litte figurines that chicks dig so much, they crack pretty easy. Noncrystalline ceramics can actually plastically deform, they deform by viscous flow. (like glaciers) The rate of deformation is proportional to the applied stress. When the ceramic coating encounters shear stress, atoms or ions slide past one another by actually breaking and reforming interatomic bonds.

Some of this information was paraphrased from:
Materials Science And Engineering, An Introdution.
Author: Callister, William D. Jr.
Published by: John Wiley & Sons, Inc. 1994
 

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We experimented in the Army with ceramic coatings on the exhaust ducts of helicopter turbine engines. We had a very bad problem with cracks in some of these ducts due to the thermal expansion cycle. We had one duct on one aircraft ceramic coated, 9 years later it is the only duct that has not ever cracked. The army didn't buy off on the coatings because it was our idea and not the Army's but believe me this stuff works. The internal surfaces on some advanced turbines also are ceramic coated.

PS. I dont want to mention the name of company that did the coating for us (Army liability stuff) but it was a major automotive coating company. They did a standard header job on our turbine duct. A photograph of our duct is even in the company's sales brochure.

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Clark
TC #68
Ft. Polk, Louisiana



[This message has been edited by Clark (edited 08-29-99).]
 
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