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View Full Version : Jet Hot Coatings WHICH ONE



JT56
12-02-2013, 10:24 AM
Well Guys my Stainless Works SBC headers have been sent to Jet-Hot twice for the 1300 Polished coating. They are telling me mine suffer from thermal oxidation and will not warranty them after this time. They are trying to get me to put a color on them? Is it possible the coating isn't good on SS? My engine is running total timing of 36 degree and 12 initial. Here is the link JetHot sent me. Tell me what you think?

http://www.jet-hot.com/coatings/premium-colors

chevynut
12-02-2013, 11:09 AM
I don't know why SS would be any different than regular steel. In fact, SS is a poorer thermal conductor than mild steel. Did they tell you why they think it's happening? I think some of the colored coatings are pretty nice.

JT56
12-02-2013, 11:37 AM
I don't know why SS would be any different than regular steel. In fact, SS is a poorer thermal conductor than mild steel. Did they tell you why they think it's happening? I think some of the colored coatings are pretty nice.

Here is their quote, "The issue that your are having is from thermal oxidation, which means they are getting too hot. A color will provide you with an added layer of ceramic coating that should handle the 500 hp motor".

Considering my winter project I am painting the firewall and fenders gold...wouldnt think a gold header would look good. Thinking of Platinum or light grey?

NickP
12-02-2013, 02:06 PM
RED! Make it pop under there!

JT56
12-02-2013, 04:27 PM
RED! Make it pop under there!


Red engine block and red headers?

Rick_L
12-02-2013, 06:16 PM
No red headers on my car, no way.

The only coating I'd consider besides the traditional is a black or black metallic, polished.

For me it's a treat that AN hose fittings and adapters are available in other than red and blue. So my headers and other coated parts won't be either.

Some of those colored coatings are not polished in the abrasive slurry that the traditional silver/aluminum coating is usually done with.

I had an intake done at Polydyn in Houston just last month. I think the silver/aluminum and a black were they only ones they had a sample of that was polished.

None of the golds or reds were polished, at least their samples. They were flat colors, looked like flat paint. Maybe others have different choices. Me, I'm happy with the traditional silver/aluminum ceramic coating look if it starts out good and endures.

They warned me that the "as cast" valleys between the ribs on my manifold might not polish out like I wanted. The guy at the shop said they had to put it back in the slurry tank for some extra time - but that part turned out fine by my way of thinking. Headers would not be a problem with this at all, except maybe that the transition between the 4 tubes into the collector would maybe take some extra time in the slurry. I don't know what the risk of making the coating too thin by excessive polishing is. My guess is that it just ties up their slurry tank a bit longer.

chevynut
12-02-2013, 07:02 PM
Honestly, I don't understand why you're having this problem. Why can they fix it with two coats? Wouldn't the base layer still peel and the outer layer oxidize? Why can't they just apply two coats of the coating you want?

reborn55
12-05-2013, 06:30 AM
Had my headers done by Jet-Hot 3 times under warranty..every time I would install them different tubes would discolor. The last time they did it they did inside and out with some new process and they still discolored. said they were running to hot in the cylinders that discolored. I could believe that if the same tubes were affected each time, but they were not. Now this was probably 12-15 years ago--I would have thought they had the process fixed by now.

Rick_L
12-05-2013, 11:46 AM
I agree with you on the different tubes logic.

JT56
12-24-2013, 02:32 PM
UPS just delivered some samples. Would rather have the polished ones but here it is. Let me know your opinion.

Joey2739

Maddog
12-24-2013, 04:10 PM
Timing is one issue, what is your A/F ratio? Too lean will run hot, especially at the exhaust port.

JT56
12-24-2013, 05:09 PM
Timing is one issue, what is your A/F ratio? Too lean will run hot, especially at the exhaust port.


Dont know the A/F Ratio, but initial timing is 12 degrees and total 36 degrees. Water temp is 180 and below.

Rick_L
12-24-2013, 07:15 PM
Some comments.

1. I'm guilty of not reading thoroughly. Stainless steel may be the problem. Stainless (or chrome) headers retain heat much longer than steel headers. I don't know how this affects the coating but it is something different from the usual coated plain steel header.

2. If you don't have vacuum advance, 12 degrees initial and 36 degrees total plus no vacuum timing is basically a retarded timing situation. Perhaps enough to make enough heat to ruin the coating.

3. Everybody thinks lean is the culprit. But if you have a rich mixture and retarded timing, the remaining mixture that was unburned in the cylinder will light off in the header. Like a torch.

4. Why coat stainless steel headers?

chevynut
12-25-2013, 09:58 AM
Rick, I gotta challenge with you on #1. Please explain what physical property of stainless steel would cause stainless headers to retain heat much longer than steel headers. Stainless steel has a much lower thermal conductivity than plain carbon steel, so theoretically if the same amount of heat is being removed from the outside surface, the surface would run cooler. The specific heat of steel and stainless steel is about the same too, but at steady state I'm not sure specific heat is even an issue. So what could possibly cause stainless headers to retain more heat?

I agree with you on #3. The other thing is that some people think that running higher octane gas will make their engine run better, even if the engine doesn't "need" higher octane. Higher octane fuel actually burns SLOWER, so in a low compression engine it could still be burning when the exhaust valve opens, wasting heat and power and increasing exhaust temperature. You should run the lowest octane that will burn without detonation under load. I have a friend with a Dodge Ram Power Wagon truck with a 8.5:1 compression Hemi. I can't get this through his head, and he keeps using premium fuel because he thinks he has a "performance" engine, so he wastes his money on high octane gas.

IMO you should be able to coat stainless headers. The reason would be to keep the color constant, since stainless and chrome like to "blue".

chevynut
12-25-2013, 10:21 AM
UPS just delivered some samples. Would rather have the polished ones but here it is. Let me know your opinion.

Joey2739

Joey, have they explained to you why they think the colored coating is going to work any better than the silver one? I don't see why it would. You mentioned they would put on two layers....so why can't they do that with the silver color you want? None of what they're proposing makes sense to me.

I like the platinum color best out of those four.

JT56
12-25-2013, 10:46 AM
Motor is 10.7 to 1 running 93 octane and sometime mix in some 107 but 1/3 of the total mixture! Not having them blue was the reason to coat them in the first place.

Rick_L
12-25-2013, 10:48 AM
Chrome headers will definitely burn you long after the engine being shut off compared to painted or coated plain steel headers. I think it's because the heat is slow to transfer across the steel to chrome layer.

I've seen the same with stainless. Maybe the heat is still transferring from the flange to the tubes after the engine is shut off. But the scientific case is harder to make. Just know what I've observed.

When I was at the coating place that I use recently, they seem to only offer a couple of colors polished, the rest are "as applied". I am with you, I can't see why there would be a difference between colors, or whether they are polished either.

JT56
12-25-2013, 01:07 PM
Joey, have they explained to you why they think the colored coating is going to work any better than the silver one? I don't see why it would. You mentioned they would put on two layers....so why can't they do that with the silver color you want? None of what they're proposing makes sense to me.

I like the platinum color best out of those four.


I am definitely at a loss why, but I like the platium the best too.

chevynut
12-25-2013, 02:35 PM
Chrome headers will definitely burn you long after the engine being shut off compared to painted or coated plain steel headers. I think it's because the heat is slow to transfer across the steel to chrome layer.

I'm skeptical ;)

Typical chrome plating has copper, nickel, and then chrome. The plating layers are microinches thick, especially the chrome layer, so heat transfer isn't affected much by the thin layers. The plated layers all have higher conductivity than steel. They're all metals, so they have resonably good conductivity...especially the copper, which is the thickest layer and it has the best thermal conductivity of any metal except silver. Nickel has much better thermal conductivity than steel or stainless steel, as does chromium (about 3 times better).

So it can't be that.

We've discussed this before, long ago, and I haven't seen any empirical data that shows that chrome parts stay hotter longer. If they do, I believe it's because it's polished and the thermal emissivity is low, hindering the radiant heat transfer.

But if a polished surface is coated, the emissivity of that polished surface under the coating has nothing to do with the radiant heat transfer, only the emissivity of the coating matters.

So imo Jet Hot is FOS. The fact that they don't just coat his headers with two coats, like they plan to do with the colored ceramic, tells me they don't understand the problem and they're grasping and hope it works. Maybe the failed surface just doesn't show up as bad. I personally think there may be some sort of adhesion problem or thermal expansion problem causing the ceramic to fail. Stainless steel has a much higher thermal expansion rate than mild steel.

JT56
12-25-2013, 03:31 PM
I going to ask, if I go with a color and I continue to have these issues, will they continue to coat them?

Rick_L
12-25-2013, 06:57 PM
The plating layers are microinches thick, especially the chrome layer, so heat transfer isn't affected much by the thin layers.

Not so, the chrome layer can be quite thick. Both industrial chrome and decorative chrome are much thicker that you are thinking. Typically .0005-.0025 thick. But that has little to do with what's going on.

You need to study up on your conduction heat transfer. Conduction through most metals is very good, but conduction between layers of different materials is far worse. So thickness is not really the big issue here anyway, it's the layers. Think of it with an electrical equivalent. It's a bunch of resistors in series. The resistance across a layer is low, but the resistance between layers is high.

You say you have no anecdotal evidence. Not so, you have mine.

For 2 years during my early dragster days, the car had a set of chromed headers. Typical deal was we adjusted the valves and checked valve springs every run or every other run. My job. I used to have the same first degree burn on my arms every week we raced, just below the elbow on the backside. Hard to avoid the upswept chrome headers when setting the valves. I probably would have been more careful if they were worse. Plus there's the fingers. Didn't burn but my fingers knew what was warm and what was hot. Threw those chrome POS away and went to a painted header and never had those burns again.

Radiant heat transfer is only a deal when surfaces are really hot. Once the surface cools to below 400-500 degrees, radiant doesn't do anything of significance, but 400-500 will definitely burn you.

My experience is that coated headers and painted headers act about the same as far as handling them after shutting off the engine.

What does all this have to do with the current coating discussion? Not sure, maybe not much.

chevynut
12-26-2013, 10:17 AM
Rick, I spent a lot of my career involved in thermal design for electronic assemblies, and I think I understand heat transfer very well.

First, decorative chrome plating is much thinner than you claim, and usually not much more than a flash to give protection and a brilliant shine to the copper and nickel layers. Copper is like a "primer/surfacer" that's used to smooth the part and is often relatively thick. Nickel is an adhesion layer between the copper and chrome. I'm sure you know that, but others reading may not.

Decorative chrome is designed to be aesthetically pleasing and durable (http://en.wiktionary.org/wiki/durable). Thicknesses range from 0.002 to 0.02 mils (0.05 to 0.5 µm), however they are usually between 0.005 and 0.01 mils (0.13 and 0.25 µm). The chromium plating is usually applied over bright nickel plating (http://en.wikipedia.org/wiki/Nickel_electroplating). Typical base materials include steel, aluminum, plastic, copper alloys, and zinc alloys.[2] (http://en.wikipedia.org/wiki/Chrome_plating#cite_note-newmoa-2)

.002 to .02 MILS is 2 to 20 microinches. Besides, chrome and the other layers beneath it have a high thermal conductivity so thickness isn't really a factor, so I agree with you there.

The thermal resistance between layers is only high if there is poor thermal contact between the layers. Electroplating gives excellent thermal contact, usually better than applied coatings, thus the resistance is low. And again, any interfacial discontinuity is extremely thin. Do you have any data or sources to validate your claim that interfacial thermal resistance is high between the plating layers? I personally don't believe that's a factor at all.

I find it hard to believe that any interfacial thermal resistance would have any measurable effect. And it doesn't even apply with stainless steel, since there's no plating. So I think your theory falls apart.

Regarding radiant heat transfer, it goes as the 4th power of the temperature difference. The hotter the surface, the more heat transfer, nd it's proportional to the emissivity of the surface. Radiant heat transfer exists at all temperatures when there is a difference in temperature between the part and surroundings. I feel a lot of radiant heat transfer from my wood stove and it's surface isn't that hot. It's also black.

I didn't say there wasn't any anecdotal evidence of what you claim. I said that there is no EMPIRICAL EVIDENCE of it that I have found, but I'm not really disputing whether it's true or not. If it's true, it's not because of thermal resistance of the plating or stainless tubes, it's something else.

Let's say you have two identical engines, one with steel headers and the other with chromed headers of the exact same design and metal thickness. You run them identically and shut them off. Let's say both headers are at the same exact temperature when the engine are shut off.

The amount of heat stored in the tubes is proportional to the mass of the tubes and the specific heat of the material. The plating is thin, so they essentially store the same amount of heat.

The only thing that could keep one hotter than the other is a difference in heat transfer off of them. There are three modes of heat transfer, conduction, convection, and radiation.

The copper, nickel, and chrome layers are thin relative to the tube thickness, and all three layers have higher thermal conductivity than the steel tubes.
I believe the interfacial thermal resistance is low. So conduction heat transfer through the tubes to the air is essentially the same. In fact, paint would tend to decrease conduction heat transfer, but not significantly.

Since both would have relatively smooth surfaces, convection heat transfer would be about the same. There may be a small difference with the polished chrome or stainless, but it's not like there are fins on the unplated headers.

So what's left? Radiation heat transfer.

The emissivity coefficient of a polished chrome surface is .058. The emissivity of polished stainless is .075. The emissivity of unpolished steel and unpolished stainless steel is around .60-.75. The emissivity of black paint is .80 and the emissivity of lampblack paint is .96. So the radiant heat transfer from the black paint surface is more than 10 times that of the polished surfaces. To me, this is the only reasonable explanation I can come up with for this phenomenon that you claim happens.

I brought this up because you have said before that chrome and stainless headers stay hotter longer, and I am trying to understand why that could happen, if it does. You also said JT's stainless headers may be the problem because of that factor. I don't think that's the case, as I don't believe they stay hotter longer unless they're polished and the polished surface is exposed to air.

sleeper55
12-26-2013, 01:36 PM
i knew there would be a book of sorta facts coming after someone discreed with cnut lmao

Rick_L
12-26-2013, 08:22 PM
Thicknesses range from 0.002 to 0.02 mils (0.05 to 0.5 µm),

Maybe sometimes, but when I see chrome coming off in chunks, leaving an edge you can see and feel, it's more like .002"-.005". That's inches. Industrial hard chrome can be even thicker.

And again, a header only has significant radiant heat transfer when the temperature is over 500* or so. The headers cool quickly to below that. I'm talking about the burning my arms and fingers, not the coating.

JT56
01-23-2014, 07:18 PM
Guys just got the Platinum Coated headers back. Here ya go.2879

reborn55
01-23-2014, 08:02 PM
Look real good---hope they work for you

NickP
01-24-2014, 09:21 AM
Guys just got the Platinum Coated headers back. Here ya go.2879

Looks black or charcoal but nice regardless.