# THERMAL WRAP ON HEADERS - YES OR NO ?



## greg69gto (May 28, 2019)

I was thinking of putting thermal wrap on my Headers (1969 GTO Engine: 400 YS). To reduce heat load in engine compartment and maybe gain some scavenging benefit.

I’ve searched through this forum but could not find discussion about this subject.

But I get comments from some mechanics to not put wrap on my Headers. I’m told that cool air needs to be around the header to dissipate the extreme temperatures that the wrap would be controlling. As the header heats up, the header wrap will slightly stretch, allowing a slight gap when the header cools. This area can now condensate. The heat on the outside portion of the header pipe is trapped between the wrap, and the small amounts of moisture that develop will cause the header to fatigue. When this moisture heats up, trapped between the heat source (header) and the wrap, it superheats.

I’m thinking to have the Headers ceramic coated instead of wrapping them. What do y’all think?


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## Jim K (Nov 17, 2020)

hey Greg,
I tried that trick of wrapping the headers with thermal wrap. everything those mechanics told you is true. Ended up having to throw out the Hooker super comps due to holes in the tubes from that issue. My second set (Doug's) were ceramic coated. MUCH better choice. Engine compartment definitely stays cooler and they helped to cure my "hot start" problem with the starter heat sinking all the heat from the Hooker's.


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## greg69gto (May 28, 2019)

Jim K said:


> hey Greg,
> I tried that trick of wrapping the headers with thermal wrap. everything those mechanics told you is true. Ended up having to throw out the Hooker super comps due to holes in the tubes from that issue. My second set (Doug's) were ceramic coated. MUCH better choice. Engine compartment definitely stays cooler and they helped to cure my "hot start" problem with the starter heat sinking all the heat from the Hooker's.


Thanks, Jim. Your comments made me better assured to go ceramic coating rather than thermal wrap the headers. Although, I did thermal wrap the starter and the oil filter, as they were very close to the headers and would gain excessive heat.


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## Old Man Taylor (May 9, 2011)

I think they are a terrible idea on a street car. It will rust the headers.


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## greg69gto (May 28, 2019)

Old Man Taylor said:


> I think they are a terrible idea on a street car. It will rust the headers.


Thanks. Seems agreement to go ceramic coating rather than thermal wrap the headers.

But, oh boy, is there a hard sell out there to thermal wrap headers.


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## Jetzster (Jan 18, 2020)

So, Is this what it does?😞😳


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## pontrc (Mar 18, 2020)

Jetzster said:


> So, Is this what it does?😞
> View attachment 138944
> View attachment 138945
> View attachment 138947


Nice headers Jet


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## Jetzster (Jan 18, 2020)

Those are known as EZ Flowes w optional cutouts, Pont😛


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## Old Man Taylor (May 9, 2011)

Jetzster said:


> So, Is this what it does?😞😳
> View attachment 138944
> View attachment 138945
> View attachment 138947


YES!


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## BearGFR (Aug 25, 2008)

greg69gto said:


> Thanks. Seems agreement to go ceramic coating rather than thermal wrap the headers.
> 
> But, oh boy, is there a hard sell out there to thermal wrap headers.


FYI the ceramic coating that header manufacturers put on isn't all that good. The way to go is to buy them in bare steel and then send them off to jet hot to have them put one of their premium coatings on it. That stuff is much better.


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## greg69gto (May 28, 2019)

There is a big pitch on selling these wraps for headers and videos out there on how to wrap headers. And I’ve seen a few cars at car shows with wrapped headers (and not just the rat rods). Notwithstanding the aesthetic issues, is anyone really seeing benefits?

So, I did some researching if race teams wrap their headers. In the past some NASCAR and other racing engine builders used header wraps for the added power gains and thermal control benefits. But the headers were disintegrating and they had to replace a high dollar set of headers after each race weekend. Only highly financed race teams could afford new headers each race and also deal with the downtime in remaking a custom set of headers.

From what I’m reading, most crew chiefs, engine builders/mechanics, and header manufacturers advise not installing these wraps. They advise to apply thermal ceramic coatings to the header material. And agree with Bear, _"buy them in bare steel and then send them off to jet hot to have them put one of their premium coatings on it"_.


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## 4856ronaldp (Nov 9, 2020)

Great stuff guys....my question is.......is heat shield a fix for break lines ?....my lines are so close to the headers i wonder if this coul d be one of many problems with my 4 piston Wilwoods ........have 65 goat.


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## Jim K (Nov 17, 2020)

Ronald,
Heat might be an issue, if it's high enough for long enough and your headers are almost touching the brake line. I am running Wilwood disk brakes also. I discovered that they don't perform near as well unless one follows their instructions closely. They have "shim" washers that center the caliper over the disk. If it's too far to one side, then only one side brake pad engages the disk with any force and stopping power is tremendously reduced. Not sure what kind of issue you're having with yours and it might be worthwhile to start another thread for your questions.


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## 4856ronaldp (Nov 9, 2020)

Hey Jimmy....that is definitley something to look into....thanks.


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## 4856ronaldp (Nov 9, 2020)

4856ronaldp said:


> Hey Jimmy....that is definitley something to look into....thanks.
> Have to add that to my list...brakes are bad....have a somewhat bumby cam...hooked up a vacuum can....reading 15 ibs. ..the numbers are a little low , but the car should stop...it slows to a stop in 20 ft.or so .....have checked booster...MC...proportioning valve...don't see a problem...comes down to trail and error...thanks again.


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## greg69gto (May 28, 2019)

4856ronaldp said:


> Great stuff guys....my question is.......is heat shield a fix for break lines ?....my lines are so close to the headers i wonder if this coul d be one of many problems with my 4 piston Wilwoods ........have 65 goat.


Do you mean Heat Shield as in a metal plate providing protection (deflection) from a radiant heat source (i.e. the exhaust pipes)? If so, then if you'll need space, the *proper material* and a means to *securely* affix the Shield - all in a tight space.

But if you meant wrapping the brake line with a thermal wrap then that may be an easier approach.


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## 4856ronaldp (Nov 9, 2020)

Hey Greg........yes thermal wrap by ''Heatshield''....having brake problems.went with Wilwood 4 piston calipers in the front.....going thru a trail and error process on why the car dosen't stop. have a bumpy cam,rigged a vacuum can ..pressure is at 15 lbs....not good but still should stop the goat...it slows to a stop....the booster,mc,prop. valve all seem to check out....its possible that the calipers are not centered over the discs....might need ''shim'' washers?....thanks again Greg...any more suggestions would help...i have the winter to figure this out.


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## Machinest-guy (Jul 19, 2019)

greg69gto said:


> I was thinking of putting thermal wrap on my Headers (1969 GTO Engine: 400 YS). To reduce heat load in engine compartment and maybe gain some scavenging benefit.
> 
> I’ve searched through this forum but could not find discussion about this subject.
> 
> What do y’all think?


Good afternoon, I've some experience in this area. I started thermal wrapping headers about 1980 soon after the material was first introduced to the automotive aftermarket after development in the aerospace industry. Header failure often occurred after wrapping if thermal loads into the header metal were excessive. Water has no bearing on header failures nor does rust. Water is gone from the area and wrap by 220 F. Rust forms a modest insulation layer which seldom goes more than .030 deep, then stops progression, unless aggravated by chemicals (road salt, etc). 220 degrees is well under the failure point of metal or the wrap. 

"Header temperature" depends a lot on where the measurement is taken. It drops about 100 degrees per inch from the port for the first foot on 1 3/4 inch tubing. If in the exhaust port you measure 1600 degrees at WOT, two inches out, generally the closest point you'd mount a pyrometer, you be at 1400 or maybe a bit less. If your port tempuature goes above 1600 for long you are going to have other problems to solve a lot quicker than header failure. 

Steel headers can constantly withstand about 1200 degrees before failure. Running temperature at idle is about 700 F and soon climbs past 1200 F. at speed. If you run at high speed expect header failures. Wrapping the headers with thermal barrier material holds heat in the metal potentially bringing an average metal temperature up to near its melting point and above its alloying temperature. The carbon in the steel can react with atmospheric oxygen and exhaust gasses to form a pot metal similar to cast iron which is weak and has a rectangular crystal structure. It falls apart from the outside in as shown in your photos.

If the inside of the header is 1400 degrees expect the outside surface to be about the same at a constant load - the coating cannot eliminate heat energy it can only resist conduction, hence averaging a surface temperature down a couple of hundred degrees if the engine produces a varied heat input - as in a road race car.

Because steel headers are operating at nearly their maximum allowed design temperature, if your engine tune and use drive peak thermal inputs past 1200 F very long or often, an upgrade in material is indicated. Typically this is into a stainless steel alloy which adds about 200 degrees before the metal starts to melt and be hot enough to reform its shape. And stainless steel can nearly eliminate the problem of reactivity with atmospheric oxygen thus preventing structural failure.

Most "thermal coating" offered by header manufacturers is based on low grade natural silica added to high temperature resistant paint. It resists some heat conduction from the header metal to air but it's main preservation function is preventing oxygen reacting with hot steel tubing to form burnt coked iron thusly preserving the header itself. To gain benefit of slightly lower thermal conduction into an engine compartment, the compartment must be vented better. The energy must exit the area somehow and airflow is how that happens. The amount of temperature drop inside an engine compartment needs to be measured with the hood shut, at speed, not subjectively when stopped and opened.

A few companies offer a ceramic coating process with high grade silica ceramic sputter welded in an aluminum base. Swain Coating comes to mind. When applied to a stainless steel header which is properly supported and designed with thermal expansion joints to prevent cracking, an exhaust header can be made which will withstand 1600 degrees a few feet down the pipes (nearly to the collector) for many 10's of thousands of miles.

I'd suggest the following guidelines for successful header installations:

1200 degrees or less at 2 inches out of the port, use steel header and paint with VHT. 
1200 degrees or less at 2 inches out of the port, use steel header and paint with VHT then add a thermal blanket laid over the headers at the flange so air can blow under and around tubes while moving. This will protect wiring and hoses. 
1200 degrees or more up to 1400 degrees, use typical thermal coating with low grade silica. Add a blanket if you need to protect wires or hoses or add a specific wrap to each component. 
Above 1400 degrees switch to stainless header materials, upgrade your header design to include stress management for anti cracking and support. Add high grade ceramic coating to protect under-hood components from premature failure. 

Benefits of exhaust scavenging occur because of high exhaust gas velocity. If the pipes cool off indicating energy loss to the atmosphere, then you'll have denser, heaver, exhaust gasses moving slower, preventing evacuation of the cylinder when the exhaust valve is open. I can't remember what the factor is - so many degrees per foot drop = density change and resistance to flow increase. But I do recall that to pick the flow up again you can reduce the pipe size. This is what most manufactures do. Example: if a head pipe is 2 1/2 inches at the manifold junction then it will reduce to 2-1/4 at the muffler, then reduce again at the muffler exit to 2 inch tail pipes. A rule of thumb was reduce 1/4 inch per 6 - 8 feet of pipe. Or ceramic coat the whole exhaust system to keep the gases flow hot and fast to the exit point. 

For shields to work they need a material of low thermal conductivity, like abstostos sheets of old, and air flow to carry off radiated heat. Without both factors you are not really doing too much to help. 

Or just drive slower and never open the throttle. If you don't burn fuel, pipes will never get hot. 

I hope this helps. Ladd


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