Temp differences, coated headers vs not coated
08-10-2018, 04:06 PM
#1
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 didn’t need a heat gun to tell the difference in the test cell.
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 didn’t need a heat gun to tell the difference in the test cell.
08-10-2018, 04:31 PM
#3
TECH Resident
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.
08-10-2018, 04:51 PM
#4
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.
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.
08-10-2018, 05:04 PM
#5
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.
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.
08-10-2018, 10:08 PM
#6
TECH Veteran
It's really a big temp difference between those two. Good thread Pooter 
08-11-2018, 08:47 AM
#7
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.
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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08-13-2018, 01:36 PM
#10
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
Agreed and the heat does help with the cats and the 02 sensors too
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.
YUUUUGE difference.
I'll have to click on that after lunch, appreciate that link!
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.
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.
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.
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.
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.
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.
08-13-2018, 06:35 PM
#15
TECH Senior Member
And the header wrap will ASSURE you of rotted headers in far less time than they'd last unwrapped.
08-13-2018, 07:41 PM
#17
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 - 1400°F 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.
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.
08-13-2018, 08:22 PM
#18
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 - 1400°F 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.
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.
08-13-2018, 10:32 PM
#19
TECH Resident
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.
08-14-2018, 08:47 AM
#20
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.
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.