Headers and Wrapping - How "On Point" is this article?

B6/7 S4/RS4
#1

I posted this on AZ but figured I’ll post it here and get better TECHNICAL advice/answers. The title pretty much says all, Headers (whether JHM V1/V2 or other platform headers)…is it a bad idea to wrap them as the article reads?

Here is the article:

http://www.centuryperformance.com/exhaust-header-heat-wraps-do-not-use.html

In one paragraph, author says this:

“Cool air needs to be around the header, and insulating it with a wrap to hold exhaust heat in makes the header material surface temperatures reach near molten levels. When you wrap the header you trap the heat in the header, but also suffocate the material that needs to breathe to dissipate heat for it’s own survival.”

But in the next (directly after actually), author writes this:

“Engineers, Metallurgists, and other experts out there will state that there is no way that the material can fail because it was designed to withstand the internal temperatures of exhaust gases. This is very TRUE! But, when the header is not allowed to cool (or breathe) so as to dissipate those extreme temperatures that the wrap is controlling, you have now developed a heat absorption that compares to thermal friction. This causes temperatures to continue to rise beyond the normal exhaust gas temperatures (EGT’s) the header material was designed to withstand. This holds true as with most any type insulation.”

Thoughts from the tech gurus?
Thoughts from JHM?
Thoughts in general?

#2

I don’t think it’s a black & white answer. I glanced over the article and generally agree, but it sounds more like an advertisement for Jet-Hot…

A few points (IMO):
-First and foremost, it depends on the particular material & thickness used in production. Period.
-It also depends on the design. In the article, they reference NASCAR…well I’m quite sure the folks who designed those headers didn’t leave much on the table in regards to weight. They would need to be redesigned if they are to be wrapped.
-The issue is really hot-spots that develop in areas where the wrap spans multiple runners. If those are also structural points, then you’re adding risk to your system.
-Turbo cars will hit EGTs much higher than NA folks will…people design parts for them to withstand these conditions (see point #1)
-I ceramic coated mine…not because I felt there was a design issue, or because I didn’t want to wrap them. I don’t believe anyone has wrapped a set of OE RS4 headers, and I’m not going to be the guinea pig. but…if I can reduce under-hood temps, I’ll do it. Hence, coating them.
-When referring specifically to the JHM design, I’m pretty sure I’ve seen quite a few cars with their’s wrapped. It wouldn’t surprise me at all if they were simply over-engineered, as JHM knew their headers would see much higher power levels as time went on. Maybe someone can chime in, are they 429 stainless? Wall thickness?

#3

321 SS

#4

If the headers are designed correctly to withstand the vehicles EGTs to begin with, insulating/wrapping them won’t hurt. Now if they are designed with the assumption of a certain amount of cooling (radiation and/or convection -air flow- over the exterior) then wrapping them might be not such a good idea.

What are the exhaust gas temps for an S4? Probably not that high especially without a turbo I am guessing. 321SS melts at ~2500F. Obviously you lose mechanical integrity as you approach the melting point but again that is a design question.

But you are not going to heat the headers beyond the EGTs simply by wrapping them. Something like the, oh I don’t know, 2nd law of thermodynamics, prohibits that. This little line “This causes temperatures to continue to rise beyond the normal exhaust gas temperatures (EGT’s) the header material was designed to withstand. This holds true as with most any type insulation” is BS IMO. And if that is BS how accurate is the rest of the article?

#5

you can tell AR is where the technical guys are. Great posts koolade is always spot on beem is right I know the headers are 321 and badger caught a important line. The article is full of semi facts but its more a point article. Where its not really stating facts but trying to make points.

The entire concept is to keep the heat in the exhaust as it helps aid the exhaust in exiting quickly. If you coat the headers or wrap them your still keeping them from expelling as much heat as they normally would. Your putting a coating on them or covering on them.

some of the article is correct but on a na car your going to get high temps for a few seconds and the second you pull of the throttle the exhaust is going to cool by almost 800deg within seconds. The good for you part is that people me included have had there JHM headers wrapped for years with no issues. The china knock off headers if you wrap them they crack in a few months. so there is a point to where if the parts are cheap and you wrap them they can break down but with the JHM headers your getting what you pay for. And wrapping them isnt an issue