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Temp differences, coated headers vs not coated

Old 08-10-2018, 04:06 PM
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Default Temp differences, coated headers vs not coated

I was browsing a hot rod header test article and this really surprised me. I've never seen anyone cover this before. Figured yall would like to see.

I know most of yall don't run painted headers, but I wonder if the temp difference is just as severe with stainless vs coated. My guess is that it would be, and I've really been eyeballing stainless headers for the truck...

From Hot Rod:

Coatings: Are They Worth It?
As a part of our test, we wanted to quantify the benefits of a coated header versus a plain uncoated black painted header. A thermal barrier ceramic coating adds considerably to the price of any header, often doubling the price. We tested two otherwise identical Hooker 1⅞-inch headers with surprising results. Running on the dyno, we found the power numbers virtually unchanged (see Average Power table on next page). Where the ceramic coating made a remarkable difference is in the heat transferred by the header. We tested the header temperature immediately after a run, and then one minute after shutdown. The coated headers measured 258 degrees F dropping to 195 degrees F a minute after shutdown. In contrast, the uncoated header measured a scalding 870 degrees, retaining 520 degrees a minute after shutdown. We didnt need a heat gun to tell the difference in the test cell.
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Old 08-10-2018, 04:16 PM
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thats why i paid extra to have my kooks coated
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Old 08-10-2018, 04:31 PM
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Coated headers are almost a necessity on swaps with small engine compartments to prevent melting things. There's also a theory that trapping the heat better can help with cat efficiency which tends to be an issue when long tube headers move them further from the engine. The only real downside is the insane cost and the questionable quality from some of the companies that do the work.
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Old 08-10-2018, 04:51 PM
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I don't have before and after measurements, but I can tell you coated stainless headers in my truck, seem to run about the same temperature under the hood as the stock manifolds.

Stainless conducts heat a little less than half as well as mild steel. In other words it's a heat insulator all by itself. Coating is obviously a further improvement.
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Old 08-10-2018, 05:04 PM
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Originally Posted by RB04Av View Post
I don't have before and after measurements, but I can tell you coated stainless headers in my truck, seem to run about the same temperature under the hood as the stock manifolds.

Stainless conducts heat a little less than half as well as mild steel. In other words it's a heat insulator all by itself. Coating is obviously a further improvement.
That's what I was wondering about the stainless.
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Old 08-10-2018, 10:08 PM
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It's really a big temp difference between those two. Good thread Pooter
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Old 08-11-2018, 08:47 AM
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https://www.engineeringtoolbox.com/t...ity-d_429.html

The whole site is a treasure trove of valuable info.

I'm not absolutely sure, but I suspect you could use the "porcelain" value in this table, to grossly estimate the effect of ceramic coating... looks like if you had stainless vs mild steel of equal thickness, you'd conduct about 40% or so as much heat; then a few .001"s of coating on top of that, could cut it about in half, more or less. I.e. coated stainless = about 20% as much heat transfer under the hood, vs uncoated mild steel, ceteris paribus.
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Old 08-11-2018, 11:25 PM
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Interesting, except that the coating on my Hookers began to fail after 3 months. The coating on the top half of the headers was there but the bottom half were rusted pretty badly. Skip Hooker and get a better brand.
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Old 08-12-2018, 10:26 AM
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Agreed: I will NEVER AGAIN buy a set of headers other than stainless.
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Old 08-13-2018, 01:36 PM
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Originally Posted by sjsingle1 View Post
thats why i paid extra to have my kooks coated
Man I don't think I'd every spit out the coin for kooks, and if I did I'd have a hard time coating them, I love the look of raw stainless

Originally Posted by bammax View Post
Coated headers are almost a necessity on swaps with small engine compartments to prevent melting things. There's also a theory that trapping the heat better can help with cat efficiency which tends to be an issue when long tube headers move them further from the engine. The only real downside is the insane cost and the questionable quality from some of the companies that do the work.
Agreed and the heat does help with the cats and the 02 sensors too

Originally Posted by RB04Av View Post
I don't have before and after measurements, but I can tell you coated stainless headers in my truck, seem to run about the same temperature under the hood as the stock manifolds.

Stainless conducts heat a little less than half as well as mild steel. In other words it's a heat insulator all by itself. Coating is obviously a further improvement.
Thanks for the before and after info, I've always had coated or painted headers. The painted headers I had came on a truck I took in trade many years ago and I didn't have it long so I didn't pay attention to the under hood temps and didn't have a before to compare it to.

Originally Posted by Tuskyz28 View Post
It's really a big temp difference between those two. Good thread Pooter
YUUUUGE difference.

Originally Posted by RB04Av View Post
https://www.engineeringtoolbox.com/t...ity-d_429.html

The whole site is a treasure trove of valuable info.

I'm not absolutely sure, but I suspect you could use the "porcelain" value in this table, to grossly estimate the effect of ceramic coating... looks like if you had stainless vs mild steel of equal thickness, you'd conduct about 40% or so as much heat; then a few .001"s of coating on top of that, could cut it about in half, more or less. I.e. coated stainless = about 20% as much heat transfer under the hood, vs uncoated mild steel, ceteris paribus.
I'll have to click on that after lunch, appreciate that link!

Originally Posted by wannafbody View Post
Interesting, except that the coating on my Hookers began to fail after 3 months. The coating on the top half of the headers was there but the bottom half were rusted pretty badly. Skip Hooker and get a better brand.
Odd, I had coated hookers on my camaro and I bought them used, the coating looked practically new when I got them and still did 5 years later when I sold the car.
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Old 08-13-2018, 05:17 PM
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So what temps do stainless SE headers get to after coating and baking with VHT rattle can? Someone test it out?
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Old 08-13-2018, 05:24 PM
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I had coated Hookers, the coating rusted off.
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Old 08-13-2018, 05:30 PM
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Originally Posted by qweedqwag View Post
I had coated Hookers, the coating rusted off.
Wonder what the difference was with yours and wannafbody's vs mine. Mine help up really well.

I had mine from around 2007-2012, they were used when I got them so they were probably made in 05 or so


Originally Posted by 5.7stroker View Post
So what temps do stainless SE headers get to after coating and baking with VHT rattle can? Someone test it out?
Go for it, let us know.
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Old 08-13-2018, 05:54 PM
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Suggestion. Use header wrap and you will be able to touch the header and leave no skin. Good for about 10 ponies also, and sometimes more.
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Old 08-13-2018, 06:35 PM
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And the header wrap will ASSURE you of rotted headers in far less time than they'd last unwrapped.
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Old 08-13-2018, 07:09 PM
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I think you can wrap stainless headers without issue.
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Old 08-13-2018, 07:41 PM
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Stainless, it mostly makes to crack. Eliminates any chance for the metal to cool. Raises the temp of the metal to more nearly exhaust stream temp. (exh is in the 1200 - 1400F range)

Wrapping is BAD BAD BAD BAD for a street driven car. Might be OK for a race-only one; not good for real long-term running.
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Old 08-13-2018, 08:22 PM
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Originally Posted by RB04Av View Post
Stainless, it mostly makes to crack. Eliminates any chance for the metal to cool. Raises the temp of the metal to more nearly exhaust stream temp. (exh is in the 1200 - 1400F range)

Wrapping is BAD BAD BAD BAD for a street driven car. Might be OK for a race-only one; not good for real long-term running.
My SS headers have been wrapped on my street-driven 04 GTO since 06. Never had a problem. Indeed, I wore the original wrap to sheds and replaced it in 2016. The pipes were tarnished but in excellent condition. Believe the internet gurus if you chose, but that is my real life experience. In addition, the wrapping cost $50 in 06 and about $70 ten years later.
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Old 08-13-2018, 10:32 PM
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Every header I've ever seen that was wrapped had something wrong with it. Just because you think it looks fine doesn't mean it actually is. The metal needs to breath and it also needs to dry off after puddles and snow splash up there. The wrap prevents both of those from happening as efficiently as possible. Whether it helps on a modern fuel injected engine is questionable anyway. It was good back in the day to prevent evaporation from the carb between runs.
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Old 08-14-2018, 08:47 AM
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Originally Posted by bammax View Post
Every header I've ever seen that was wrapped had something wrong with it. Just because you think it looks fine doesn't mean it actually is. The metal needs to breath and it also needs to dry off after puddles and snow splash up there. The wrap prevents both of those from happening as efficiently as possible. Whether it helps on a modern fuel injected engine is questionable anyway. It was good back in the day to prevent evaporation from the carb between runs.
This isn't about mud puddles or for the purported need for steel to breath. Its not about fuel evaporation either. Wrapping the header raises exhaust temps. The cold air acts like a barrier to the exhaust flow. When 1200 degree exhaust gas leaves the port, it flows into the exhaust manifold. The typical manifold is cast iron and heats up to 400-500 degrees. The temperature difference acts as a barrier and requires more force to push out the exhaust.

When wrapped, this raises the temps of the exhaust manifold and makes it easier for the expanding gases to escape. This then requires less force from the crank and piston to push out the exhaust gas.
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