Exhaust header wraps

[Howard]

Is this article bogus?

http://www.350z-tech.com/zwiki/Header_wrap_vs_Header_coating

 

[Demon-Xanth]

I've always heard basically that. The wrap holds in moisture and tends to promote degradation. If you're running a sprint car and will swap them out after a year it's not a big deal. especially since they come off on a regular basis anyways. But if you have a street car (ever installed headers on a street car?) it's a bad idea.

 

[Throckmorton]

I don't know anything about headers but it sounds reasonable that they would cause damage by trapping heat.

But this statement makes no sense...

Jet Coat and other companies use a process which actually becomes part of the material of the header. Example. the header is allowed to cool normally because there is no thermal barrier trapping the heat in (header wrap) but the coating acts like the thermal wrap in that it helps to reduce the amount of heat into the engine bay. Wierd huh? Not really.

Yes it is weird, and apparently the author of this doesn't understand basic physics. Every unit of heat you keep out of the engine bay is retained in the header, you can't have it both ways. Either you're insulating more than stock or you're not...

People who don't know what they're talking about should refrain from writing articles.

 

[Iron Woode]

I don't know anything about headers but it sounds reasonable that they would cause damage by trapping heat.

But this statement makes no sense...


Yes it is weird, and apparently the author of this doesn't understand basic physics. Every unit of heat you keep out of the engine bay is retained in the header, you can't have it both ways. Either you're insulating more than stock or you're not...

People who don't know what they're talking about should refrain from writing articles.

he is correct.

The coating is bonded metallurgicaly to the header and reduces engine bay temps. There is no air space trapped against the header like there is in header wraps.

This keeps more of the heat inside the header and hence in the rest of the exhaust system.

 

[PlasmaBomb]

But this statement makes no sense...


Yes it is weird, and apparently the author of this doesn't understand basic physics. Every unit of heat you keep out of the engine bay is retained in the header, you can't have it both ways. Either you're insulating more than stock or you're not...

People who don't know what they're talking about should refrain from writing articles.

^ This. The author is an extremem idiot...

 

[PlasmaBomb]

he is correct.

The coating is bonded metallurgicaly to the header and reduces engine bay temps. There is no air space trapped against the header like there is in header wraps.

This keeps more of the heat inside the header and hence in the rest of the exhaust system.

No he isn't the coating is itself a thermal barrier... so when he says there is no thermal barrier he is wrong. He may mean something else, but that isn't what he said.

 

[Gillbot]

not to mention header wrap can cause cracking. it happens on a lot of turbo cars that use wraps.

 

[thomsbrain]

The cracking is usually caused because you're only retaining heat on one side of the header when you wrap the outside. Thermal coats usually are applied to both the inside and outside of the header, meaning heat exchanges happen at the same rate (percentage wise) as they do with a bare header, so they shouldn't be any more likely to crack.

 

[Howard]

The cracking is usually caused because you're only retaining heat on one side of the header when you wrap the outside. Thermal coats usually are applied to both the inside and outside of the header, meaning heat exchanges happen at the same rate (percentage wise) as they do with a bare header, so they shouldn't be any more likely to crack.

What difference does it make?

 

[Bartman39]

Thermal coatings keep the headers from forming corrosion... Also allow for much higher operating temps with turbo`s and such... The best part is how they look... :thumbsup:

Also a long time ago they had headers that were coated with aluminum it was in a powder form and was heat applied and was the early basis for the jet hot coatings & process... The aluminum would come off after time but it was pretty cool to work around you could do so and not get scorced or a sizzle burn even while the engine was running you just knew it was getting pretty hot without the painful burns... Blackjack, Cyclone & a few other brands made them, but dont think anyone does now...

 

[Iron Woode]

No he isn't the coating is itself a thermal barrier... so when he says there is no thermal barrier he is wrong. He may mean something else, but that isn't what he said.

I know.

He's just not stating it very well. Maybe he sniffed too much exhaust fumes.

Here is what he is trying to say:

header wrap traps some of the heat but allows moisture to develop against the outside of the header when it cools. It also causes uneven cooling of the headers.

The coatings provide a better insulating effect and because it's part of the header it protects it from corrosion and allows a more even cooling for the headers.

The coatings reduce engine bay temps.

There, I said it better than he did.

I am now looking for a place around here that does these coatings. The only one I have found so far is :

http://www.fireballcoatings.com/index.php

 

[ebaycj]

I don't know anything about headers but it sounds reasonable that they would cause damage by trapping heat.

But this statement makes no sense...


Yes it is weird, and apparently the author of this doesn't understand basic physics. Every unit of heat you keep out of the engine bay is retained in the header, you can't have it both ways. Either you're insulating more than stock or you're not...

People who don't know what they're talking about should refrain from writing articles.

Or, the ceramic coating acts as insulation.

This keeps more of the heat in the exhaust gas, rather than transferring to the metal of the headers, and then radiating that heat into the engine bay.

 

[ebaycj]

I know.

He's just not stating it very well. Maybe he sniffed too much exhaust fumes.

Here is what he is trying to say:

header wrap traps some of the heat but allows moisture to develop against the outside of the header when it cools. It also causes uneven cooling of the headers.

The coatings provide a better insulating effect and because it's part of the header it protects it from corrosion and allows a more even cooling for the headers.

The coatings reduce engine bay temps.

There, I said it better than he did.

I am now looking for a place around here that does these coatings. The only one I have found so far is :

http://www.fireballcoatings.com/index.php

Perfectly said.

 

[speedy2]

The easiest way to tell if a modification is crap?

Go to a carshow/shop where there are high performance cars. Or cars that have been intensely modified. How often do you see header wrap?

Now, go to a ricer car show. Now how much header wrap do you see?

 

[PlasmaBomb]

What difference does it make?

Think of an oxyacetylene torch (this represents the hot exhaust gases from the engine) - apply it to a sheet of metal, it will glow red hot and if the flame is hot enough you will melt the metal.

Think of insulation on the engine bay side of the header as a heat proof mat (like you used to get in science classes) clamped behind the metal. What is going to happen when you apply the torch?

The metal is still in direct contact with the heat source, and if anything it's ability to dissipate heat is reduced. It will get hot and is more likely to melt...

Now think of a ceramic coating on both sides of the header as a heat mat in front of the metal sheet (and behind it...) - the metal is no longer in direct contact with the heat source and since the mat is a good insulator (like ceramic coatings) the heat transfer from the exhaust gas to the metal is reduced - you would be doing well to get the metal glowing red hot!

Of course you could use a flame (exhaust) hot enough to burn the mat... but then you would probably have problems with the engine internals...

I didn't know that places offering ceramic coatings did the inside and outside... I would certainly check as an external coating would probably be marginally better than a wrap for the headers life expectancy.

 

[Apex]

I didn't know that places offering ceramic coatings did the inside and outside... I would certainly check as an external coating would probably be marginally better than a wrap for the headers life expectancy.

Yep, entire thing is coated. This is a set done by Jet-Hot in black:

Typical surface tests:

 

[Gillbot]

Typical surface tests:

Take those readings with a grain of salt. I can tell you now they are using that device improperly to read temperatures. If you want to get a real reading, you need to use a contact probe, not a cheap-o IR thermometer which ready mostly reflected energy due to the coating.

 

[Howard]

Take those readings with a grain of salt. I can tell you now they are using that device improperly to read temperatures. If you want to get a real reading, you need to use a contact probe, not a cheap-o IR thermometer which ready mostly reflected energy due to the coating.

Generally IR thermometers can be quite accurate as long as the surface you're reading has a 0.95 emissivity (what they are usually calibrated for).

 

[Gillbot]

Generally IR thermometers can be quite accurate as long as the surface you're reading has a 0.95 emissivity (what they are usually calibrated for).

Emissivity and angle take a large toll on reported temperature and MOST people do not use the IR thermometers correctly. As you can see in the pic above, they are shooting temps at a high angle on a rusty header vs. a nice shiny coated one. Many of the coatings use metal flake so I highly doubt they are shooting at a very emissive surface.

 

[RGUN]

The easiest way to tell if a modification is crap?

Go to a carshow/shop where there are high performance cars. Or cars that have been intensely modified. How often do you see header wrap?

Now, go to a ricer car show. Now how much header wrap do you see?

I run wrap, based on research and discussions with a few people, some of whom are very active racers, others who work pit crew with the Nascar circuit, and others who build and race rally cars, they prefer the Wrap. I know of several top performing drag cars who run wrap only, and racers who run wrap only or both. Their results all seem to indicate that the wrap reduces underhood temperatures the most. Best case scenario I wouldnt have to run anything and just use the stock heat shield - but running an equal length header on my Subaru put the headers about 1/2" from the oil pan, and with cruising EGT's hitting 1400F and on throttle 1600F, I needed to protect my oil from cooking. So wrap it was. (also, my tuner has seen several cases of coated headers / up pipes flaking some coating and having it damage a turbo).

 

[speedy2]

I wouldn't doubt any of that, but that's pretty specific and also in racing applications. A ricer with 140HP with wrap is just funny when I see a ton of 400-500HP street cars without it. lol

 

[Apex]

Take those readings with a grain of salt. I can tell you now they are using that device improperly to read temperatures. If you want to get a real reading, you need to use a contact probe, not a cheap-o IR thermometer which ready mostly reflected energy due to the coating.

That makes sense.

In general, I've seen quite a large temperature improvement with coatings, especially with turbocharged applications.

 

[Demon-Xanth]

RGUN: Like I stated though, longevity in racing and longevity on the street often mean two different things. No big deal for a race team to go through headers every couple years. 🙂

 

[RGUN]

RGUN: Like I stated though, longevity in racing and longevity on the street often mean two different things. No big deal for a race team to go through headers every couple years. 🙂

Well, my vehicle is driven year round in Ontario, Canada with lots of snow and salt on the road. I have thin wall stainless steel headers. Ill let you know how it holds up, next spring everything is coming out for a new block, so I will unwrap and inspect at that time.

 

[Gillbot]

Generally IR thermometers can be quite accurate as long as the surface you're reading has a 0.95 emissivity (what they are usually calibrated for).

as seen here: http://www.ib.cnea.gov.ar/~experim2/Cosas/omega/emisivity.htm

Steel, Unoxidised at 212 (100) = .08
Steel, Oxidised at 77 (25) = .80

There's a large variance there, plus emissivity also changes with temperature. Those cheap-o IR thermometers are good for a "ballpark" number but aren't anywhere near accurate.

Once you get below .7 or so emissivity, temps can't be reliably read.