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!"
- Header wraps are designed to keep the heat in the header to improve
scavenging of the cylinders. Keeping the heat in the header allows the
exhaust speed to remain high. (the right idea)
- Header wraps, by keeping the heat in the header, also reduces the radiant heat in the engine bay.
- There are no header manufacturers that I know of who will warranty
their headers if header wrap has been installed on their products. This
includes partial installations of the header tape on certain tubes or
- In most cases, the header wrap damages the headers beyond repair.
- If you run a lean mixture, you "may" see a slim performance gain
using header wraps, but not as much as a ceramic coating. A rich mixture may show slim to absolutely NO gain
- If replacing your headers and header gaskets regularly does not
bother your wallet or your time, and you like that ugly look of a
wrapped header, go ahead and use the heat wrap.
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
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!
TEMPERATURE READINGS, TAKEN AT DAYTONA MOTOR SPEEDWAY:
Below are the test parameters and results using both Jet-Hot Coatings® coated and uncoated headers:
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
- 450º F.
2" above header port (on header)
- 90º F.
1" above floor pan (in car)
- 50º F.
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.
SOMETHING ELSE THAT FEW RACERS and CAR OWNERS REALIZE:
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:
- Mild Steel (1010) uncoated header exposed to continuous 1200º F. in
normal air will have a weight loss percentage of roughly 25% with only
10 hours use at this temperature.
- Stainless Steel (410) uncoated header will have roughly 8% weight loss in the same 10 hour period.
- A coated mild steel header will have NO weight loss at temperatures
up to 1200º F. In fact it will actually gain a bit of weight! Between
1300º F and 1600º F the coating will begin to show signs of mud cracking
or like the look of lacquer checking. However, limited diffusion takes
place between the coating and the substrate, producing a very thin film
of iron aluminide, which continues to inhibit oxidation.
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!
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