Exhaust Header Heat Wraps - Do Not Use

taken, in part, from an article by Century Performance

Why Header Wraps Destroy Your Headers ... and Why Thermal Ceramic Coatings are Recommended  

We are regularly asked, or have commented on the use of header wraps (header tape, thermal tape, heat tape) on exhaust header systems. This issue is a real pet peeve of mine. Good or bad about a product I will give my opinion based upon direct use and fact, and this stuff screams "Do Not Use on Exhaust Headers!"
In the past, almost all NASCAR and other racing engine builders and crew chiefs used header wraps for the added power gains and thermal control benefits offered by their use. Problems occurred when these same teams had to replace the headers after each race (NASCAR) due to the wrap being about the only thing holding each header together. Most engine builders, crew chiefs, and definitely the header manufacturers themselves do not promote the practice of installing these wraps directly on the headers! They now utilize the advancements brought forth by thermal ceramic coatings that are chemically and electrically applied to the header material. Popular header coating services include Airborn, Jet Hot, HPC, and some header manufacturers (Sanderson Headers for example) now apply theese thermal coatings in-house.
Imagine having to replace a set of headers after each race weekend! Few but the most financially well-off race teams can afford to do this. Also consider the downtime in remaking a custom set of headers. Most custom header manufacturers do not have copies readily available. 
I believe that the wraps are good to protect various underhood 'items' from heat, but not for the use of holding the heat in the header. For example: you can use the wrapping for the protection of fuel and oil lines, wiring, covering for a starter, etc. 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. Wrapping the header traps the expansive heat between the header surface and the wrap, but also suffocates a material application that needs to breathe to dissipate heat for its own survival.
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! However, when the header is not allowed to cool (or breathe) so as to dissipate those extreme temperatures that the wrap is controlling, it now develops a heat absorption response that compares to thermal friction. As the header heats up and expands, stretching the header wrap slightly, it allows a slight gap when the header cools. This area, even though very small can now condensate (sweat). 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.
Try this experiment the next time you launder a load of bath towels and then dry them. Immediately pull them out of the dryer and just toss them in a snug pile on your bed. Now leave them there for a many hours, even a day, and then open them. You will find that there is still a considerable amount of heat left in the center towels. This heat, even though the outer towels and bed are normal room temperature have been able to contain their heat. This is a simple thermal insulation test, but compared to your headers you have an internal heat supply constantly coming from the engine when running. The freshly dried bath towels do not need to breathe, your header material does.
The heat on the outside portion of the header material is trapped between the wrap, and the small amounts of moisture that develop will soon cause the header to fatigue. This build-up of heat and moisture is amplified by the wrap. When this moisture heats up, trapped between the heat source (header) and the wrap, it superheats. Another related example is the condensation that builds in a vehicle's exhaust piping. How often do we wake up on a cool morning and see the steam coming out of the exhaust pipes of our own and other vehicles. Small amounts of moisture from the air has been drawn into the cooling exhaust piping and is now being burnt off the next morning. This is not usually an issue because it burns off. In extreme cases the regular moisture can cause the exhaust piping to rust out. It is for this reason (attempts to keep moisture from developing between the header and wrap) that the header wrap manufacturers state that a tight, secure installation of the wrap is imperative. However, it will never be tight enough to prevent moisture from being drawn in!
Although the EGTs inside the header basically stay the same by the tune of the engine and use, the properties of the header material changes by amplifying the temperature from the insulation and collected moisture. This action goes against normal laws of thermal dynamics, but this effect is fact, and you have to pull the ears off most engineers before they believe you. This is the trouble with a great education, but lacking in something that is often just as important --- "common sense"! If you decide not to believe these statements that is your choice. Go ahead and install the header tape on your headers, and we'll be happy to sell you a new header set!

Below are the test parameters and results using both Jet-Hot Coatings® coated and uncoated headers:
(10 Laps; the same engine and car with identical headers; one header set is uncoated, one header is Jet Hot® coated. The engine is operated between 6,900 and 7,500 RPM, and temperatures are measured immediately after the last lap with the engine idling at 2,000 RPM with identical sustained EGT's of 850º F.)
1" from engine
300º F.
750º F.
- 450º F.
2" above header port (on header)
210º F.
300º F.
- 90º F.
1" above floor pan (in car)
115º F.
165º F.
- 50º F.
Pretty impressive difference! With any coating it is important to not damage the coating. The thermal coating becomes part of the header material. Most of the other coating brands are comparable to these figures ---as long as they are multi-layer, inside and outside of tube applied and using proper materials. NOTE: Most "inside" tube coating applications will not cover the entire inside of each tube, as they are limited by the length of the application wand. This is not a problem.


Headers Oxidize
Under normal use, and even more with higher EGTs and header surface temperatures, every header will oxidize, and small amounts of material is actually removed from the headers over time. This means that uncoated headers will become lighter and weaker over time.
Examine these actual test numbers:

Now, think about the information provided above and consider the added thermal stress generated by the header wraps. What do you see? Remember that the wrapped metal cannot cool properly and the header wrap is causing the material to super-heat and pre-maturely fail!

CONCLUSION (webmaster's) These findings match my own with 100s of Morgans over 30 years. I must also note that I am uneasy with stainless steel branch manifolds because the stainless steel process causes embrittlement. Combine this with stainless steel headers steel-bolted into an aluminum block and e have god cause for discomfort considering the low exhausts we use and back up with. Having all this and impacting those exhaust transfers the force to the engine bolts. I have encountered the problems this can cause many times with Morgans. If you need options for repair, contact me.