I had to make a custom exhaust for my naturally aspirated rotary miata. I used 14 gauge mild steel mandrel bent pipes, had them tig welded together, and painted it with some high temp ceramic paint. After running it for about 30 minutes the paint started to flake, so I heat wrapped the header portion. I've heard people say that this will promote rust, or keep internal heat in too much and cause the headers to weaken. My fab guy, who is very knowledgable with cars and different types of metal, said that I shouldn't worry about it as long as I run the car often enough to keep any collected water out of the heat wrap. On the other hand, I've also had other people whose opinion I trust say otherwise.

What do you guys think?

 

it seems like the wrap does shorten the life of mild steel, but unless you are out and out racing, mild steel seems to last decades... the header on my car now was used when i got it in the early 90's, and its fine.

so maybe wrapping it shortens the life from 50 years to 5 years, its still a long time....

 

same guage steel, my header "melted" in 500 miles with the wrap. my dad said not to do it and i did it anyway's. DA me, lesson to yer elders

melted= i blew a hole the size of a quarter about 3" from the manifold where the first bend was

 

Think about it. The wrap holds the heat in, so therefore the metal gets that much hotter. Mild steel will degrade at a faster rate when exposed to higher heat. Kind of a no-brainer really.

That being said, I still think it is a good idea.

 

Why not just go about making a heat shield?

 

Lets keep thing in perspective here. Do you know your EGT's? You sure it was good quality mild steel or a mixture of something else? If we don't know these things, then others can be fooled into thinking that MILD steel isn't a reliable metal. It has a higher melting point than stainless. Simple Google search below!

http://www.auto-ware.com/techref/meltpoint.htm

 

Mild steel oxidizes a lot more than stainless. Especially when glowing. It's the heat cycling that will EVENTUALLY do the mild steel in. Depending on gauge, it could take a while.

 

cool! I'm glad to know my exhaust will probably hold up ok for a while

 

I have a stainless exhaust and I always header wrap it to keep engine bay temperatures down. It does it pretty dramatically. On the down side, I have to change the header wrap about every year, always gets burnt up. I really need to invest in some good quality ceramic coating I think.

 

I wouldn't recommend it on a vehicle that gets driven daily or see's lots of moisture because it will get trapped in the wrap when it gets wet and rot the pipe.

 

Yes, exactly. My wrapped mild steel header in the GLC steams on a cold day.

 

As long as it doesn't sit and stay damp it should be fine. Running to temp will drive
off any moisture in the wrap pretty quickly and make it good and dry again.

Its the sitting and absorbing moisture that could cause some issues. It does
dramatically reduce the radiated heat from the headers and as long as you
"drive" out the moisture on a regular basis it should be fine.

And for the guy who said he wrapped his headers and then blew a quarter sized
hole at the first bend, you had other issues and it wasn't the wrapping that
caused it. Running too rich would be my guess.

 

I have been daily driving mine and racing it quite a bit with the header wrap, for about 4 years now ... but like I said I'm stainless steel pipinh though. One of these days ill take it off and get it ceramic coated and have it fully boxed in from the engine bay with aluminum shielding.

 

My REPU header from RB had a dime sized chunk blown out of it by the previous owner at the same spot as yours. The header was not wrapped. Engine/carb had issues.

 

running too rich? wouldnt lean create more heat since fuel cools?

 

I think your climate/region makes a big difference also. I'm getting ready to wrap my headers. I already built a heat shield to cover my whole header assembly. The less heat that radiates up to your intake manifold, the more power you will make. I also have a vented hood. So I want things really really cool in my engine bay. I live in west Texas (which is a dry heat environment). I won't be having any moisture problems as the humidity levels here are very low (unless it rains of course).

 

Header wrap is the devil. Will soak up oil and start a fire in no time. Use stainless, ceramic coatings or both. Cheaper in the long run

 

http://www.performancecoatings.com/
I've done both ceramic and header wrap. I've only had one header crack on my that was wrapped, but it was a rotary engineering headerand it was over 20 years old. I recomend header wrap. Like siad it will shorten life, but it'll still last you 5 years. I currently run a ceramic coating on my ISC header and i can touch the header while the car is running. They did my header for $140. Im my oppinion it's well worth the price. It's way cooler than header wrap and much prettier.

 

I have a peripheral ported first gen RX-7 road racer that I have been running for 16 years now. After a few years of racing, I wrapped the Racing Beat header and midpipes to keep the floor of the car cooler. After about 6 months of using it with the wrap, the exhuast pipe started rubbing against the rear axle. The pipes had warped, and drew forward almost an inch at the rear axle! I had to sawzall the rear section off the pipes just to finish that road race weekend out.
After that race, I unwrapped everything to see what had happened. The surface of the mild steel RB pipes were flaking. Thin, nickel to quarter size layers of steel had oxidized and flaked off the steel pipes. They looked horrible, like leprosy. My theory is that the sustained 1700 degree exhuast temp of my road racer had overheated the mild steel exhaust pipes because they were no longer getting that 100 mph breeze of air over them to cool them down.
I pulled those pipes off my racer, and installed a stainless steel header and made a new set of mild steel mid-pipes, and those have lasted for over 7 years with no wrap and no problems. No, I did not have any carb problems.
I took the set of heavy gauge warped, leprous Racing Beat header and pipes, straightened them out, and put them on my daily driver streetport 1st gen. Those old RB pipes are so thickwalled, that they are still holding up with 7 more years of street use. Those old RB pipes are now 16 years old!

PS - when I got rid of the wrap, I fabricated a new set of heat shields for my race car. I am a mechanical engineer, and I believe that a heat shield with an air gap on each side does a better job of reducing radiant heat transfer from exhaust pipes to chassis components than the wrap does.

 

yeah i think that way works very well too. i'm doing something similar with my PP. the intake flanges are wrapped with header wrap, and someday i'll make a heat shield for the header

 

Funny that's exactly what I've done recently for my 20b. The shield I built works so well that my intake is only luke warm to the touch at the flange base. Based on the info of your post, I'm not gonna take the extra initiative and wrap my header as I now see there's no need. Thx for the info!

 

can you guys post up up pictures of the boxes you've made?

 

I wrapped my mild steel headers and am not concerned with it. When (if) it dies, I'll replace it. If you fabbed up your own headers and used a very thin steel to save money, they were going to burn through at some point anyways. Technically speaking, mild steel should probably never be used on an exhaust and especially not on a rotary. In a perfect world we would all at a minimum be running 321 stainless. Not even 304. However it is expensive so we make compromises by running mild steel. That is where the failure really is. It is in the material selection. I do it too though but I understand the tradeoffs.

You actually shouldn't header wrap stainless as it has a much larger coefficient of expansion. The more heat you hold in, the more it will expand and it will do it to a far greater effect that mild steel will. This typically leads to cracked weld joints. If the welds are sound then the cracks may develop next to them. Even stainless is not exempt to heat.

Header wrap serves a purpose and one I find to be quite useful and justifiable. Will it shorter than life of your exhaust? Of course it will. It's job is to hold in more heat and more heat affects exhaust materials. There is no magic or suprises in this. I would personally rather use it than not even knowing that a header may deteriorate quicker. If you have a decent thickness material with solid welds, it will still last several years. That's good enough for me.

 

I will as soon as I pull the engine back out. It's ugly right now but it works. I plan on making a better one later.

 

Well all of my compromises are based on lack of experience in building such items. I would rather learn with the cheap stuff 1st and upgrade later.