Exhaust Header Heat Wraps - Do Not Use

2014.6.11. Exhaust Header Heat Wraps - Do Not Use

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Exhaust Header Heat Wraps -Do Not Use

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Exhaust Header Heat Wraps - Do Not Use

Why Header Wraps Destroy Your Headers ... and

Why Thermal Ceramic Coatings are Recommended Regularly we are asked about, or have commented on the use of header wraps (headertape, thermal tape, heat tape). This issue is a real pet peeve of mine. Good or bad about a product I will give my opinion basedupon direct use and fact, and this stuff screams "Do Not Use on Exhaust Headers!"

THE FACTS:

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 that will warranty their headers if any header wrap is installed on their

products.

In most cases the header wrap damages the headers beyond repair. (I will explain below)

If you run a lean mixture, you "may" see a slim performance gain using header wraps. A rich mixture may show slim to

absolutely NO gain in performance.

If you do not mind replacing your headers and header gaskets regularly, and you like that ugly look of a wrapped header,

go ahead and use the heat wrap.

BACKGROUND INFORMATION: In the past, almost all NASCAR and other racing engine builders and crew chiefs used header wraps for the added powergains and thermal control benefits offered by their use. Problems occurred when these same teams had to replace theheaders after each race (NASCAR) due to the wrap being about the only thing holding each header together. Most enginebuilders, crew chiefs, and definitely the header manufacturers themselves do not promote the practice of installing thesewraps directly on the headers! They now utilize the thermal coatings that are chemically and electrically applied to theheaders. Popular header coating services include Airborn, Jet Hot, HPC, and some header manufacturers now applying thethermal coatings in-house. Imagine having to replace a $1500.00+ set of headers after each race weekend! Few but the most financially well-off raceteams can afford to do this. Also, consider the downtime in remaking a custom set of headers. Most custom header makersdo 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 theheader. For example: you can use the wrapping for the protection of fuel and oil lines, wiring, covering a starter motor, etc. Cool air needs to be around the header, and insulating it with a wrap to hold exhaust heat in makes the header materialsurface temperatures reach near molten levels. When you wrap the header you trap the heat in the header, but also suffocatethe material that needs to breathe to dissipate heat for it's own survival.

Engineers, Metallurgists, and other experts out there will state that there is no way that the material can fail because it wasdesigned to withstand the internal temperatures of exhaust gases. This is very TRUE! But, when the header is not allowed tocool (or breathe) so as to dissipate those extreme temperatures that the wrap is controlling, you have now developed a heatabsorption that compares to thermal friction. This causes temperatures to continue to rise beyond the normal exhaust gastemperatures (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 dryerand 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. Youwill find that there is still a considerable amount of heat left in the center towels. This heat, even though the outer towels andbed are normal room temperature have been able to contain their heat. This is a simple thermal insulation test, but comparedto your headers you have an internal heat supply constantly coming from the engine when running. The heat on the outsideportion of the header material is trapped between the wrap, and soon will begin to fatigue the header. This build-up of heat isamplified by the wrap. Your freshly dried bath towels do not need to breathe, your header material does. The EGTs stay the same but the properties of the header material changes by amplifying the temperature due to theinsulation. This action goes against normal laws of thermal dynamics, but this effect is fact, and you have to pull the ears offmost engineers before they believe you. This is the trouble with plenty of education, but a lack of something that is often just asimportant, that of "common sense"! If you decide not to believe these statements that is your choice. Go ahead and install theheader tape on your headers ... we'll be happy to sell you a new header set!

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HERE ARE A FEW TEMPERATURE READINGS TAKEN AT DAYTONA MOTOR SPEEDWAY: Below are the test parameters and results using 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. Theengine is operated between 6,900 and 7,500 RPM, and temperatures are measured immediately after the last lap with theengine idling at 2,000 RPM with identical sustained EGT's of 850 F.)

MEASURED AT: JET-HOTCOATED

NO COATING COATEDDIFFERENCE

1" from engine 300 F. 750 F. - 450 F.

2" above header port (on header) 210 F. 300 F. - 90 F.

1" above floor pan (in car) 115 F. 165 F. - 50 F.

Pretty impressive difference, and with any of these coatings you should take care to not damage the coating. The thermalcoating becomes part of the header material. Most of the other coating brands are comparable to these figures (if they aremulti-layer, inside and outside of tube applied and using proper materials).

SOMETHING ELSE THAT FEW RACERS and CAR OWNERS REALIZE:

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

Mild Steel (1010) uncoated header exposed to continuous 1200 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 1200 F. In fact it will actually gain a bit of

weight! Between 1300 F and 1600 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. Whatdo 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!

ON A SIDE NOTE:

Do you understand the physics of exhaust flow in regards to step-headers?

Step headers are designed to allow controlled and efficient exhaust gas expansion within a selected engine RPM range. Whatdoes this mean? As exhaust gases are exiting the cylinder head exhaust ports and into the header they are still burning, andthese gases are rapidly expanding down the primary tubes. In fact, they are "pulsing". If you design the header to takeadvantage of the pulse expansions of the exhaust gases you WILL gain horsepower. But, you'd better do it right, or that$1500.00 or more for a set of custom step headers is a waste of money. When you set up a step header, you'd better knowwhere you want the maximum power at, since steps are RPM specific to each engine combination.

DEFINITION: A "STEP" is an increase in primary tube diameter.Here is an example: A basic Chevrolet 350 cubic inch engine: 3.48" stroke, 5.7" connecting rod length, 4.0" bore, 10.5:1 compression ratio,standard 2.02" / 1.60" Intake/exhaust valves; designed for 6500 RPM operation. Cam specs are: .500" lift, 235 duration @.050" lift, 112 lobe centerline. For the average Joe Bracket Racer this would be a standard 1-5/8" or 1-3/4" primary header primary tube size, depending onvehicle weight, gearing, transmission type, and where you want your power. Here is the "exact" header size for a racing engineoperating at 6500 RPM. Note: This is for max power at 6500 RPM!

HEADER TYPEPRIMARY

TUBEDIAMETER

PRIMARYSTEP

LENGTH

SECONDSTEP

DIAMETER

SECONDSTEP

LENGTH

THIRD STEPDIAMETER

THIRD STEPLENGTH



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Straight Pipe 1.757" 31.9" - 34.4"

2-Step Header 1.757 " 14.0" - 16.5" 1.882" 15.4" - 17.9"

3-Step Header 1.632" 14.0" - 16.5" 1.757" 6.8" - 9.3" 1.882" 6.1" - 8.6"

Collector Specs:3.221" Diameter with a 18.0: to 23.0" length (2nd best = 9.0: to 11.5" length)Acoustical Tuning Specs:best wave = (- negative pressure) = 5,000 - 6,000 RPMsbad wave = (+ positive pressure) = 2,018 - 3,518 RPMswav-lag degrees = 3.2 - 6.3

This is a "Optimized" header design for an engine operating primarily at 6500 peak horsepower operation. The reason for adding the above step-header specs was to to let you know that the header has areas where the expansiveexhaust gases compress as they pass through the header. Or should I say the gases are not allowed to expand. As we allknow, the compression of air, or in this case compression (or restriction) of exhaust gases, will generate heat. Anywhere therestep is not properly located you will create added heat. Of course there is no "Perfect" header design unless the engine was to never change RPM. With an internal combustionengine that has an operating range from idle to well over 6,000, 8,000 or even 10,000 RPM, there is no specific header that isbest for an entire power band. You set up the step header for the RPM that the engine will spend the most operating time.

You can call this compression of exhaust gases (or restriction) that of thermal dynamic friction. You cannot have truefriction from a gas against a solid, but you can have this compressed gas as a source of added exhaust heat.

BASIC UNDERSTANDING: Because of the expanding gases, if you have had the experience (as I have) to see first hand what header warp has done to aheader, you would notice the locations on a header where the material failures occur. This is typically where a step would be,or where there is an expansion pulse of exhaust gases inside the header tube. I have had headers in my hand where literallythe only thing keeping the header in one piece was the wrap. Whole chunks of the header material was gone, simply meltedaway. If you were to speak to most "engineers" (I use that title with caution) they will probably tell you that aliens stole the metalas the car was racing around the track! They say this because the conclusion that the wrap is causing problems is not part ofnormal metallurgy and thermal dynamics theory . The header wrap allows temperatures between the wrap and theheader to turn the material molten.

IN CLOSING:

We know that header manufacturers will NOT WARRANTY a header which has had a wrap installed on it. We know that I(and many others) have personally witnessed, tested and inspected headers that have been destroyed after running headerswraps, and these headers were on a perfectly tuned engines. Just because an item or product is advertised for a specific use does not mean it does not do what the promotion oradvertisement states. But, it also does not mean it is the best choice either, or that there are negative consequences. We haveall seen TV commercials on all of these "medical miracles" and "overnight diets" that do such feats as fast weight loss and re-grow your hair. How often have we laughed at the side affects, like the most common being penile failure. Oh sure, I want totake some drug if my hair starts falling out that makes other body parts fail to function. NOT !!! Those pharmaceuticalcompanies can pucker up and kiss my backside! I'd rather have function than hair! The same can hold true with automotive and marine products. Heat wraps are great, just do not use them ON the header.Use them on a device or component on your vehicle that you are trying to protect from header heat. If you want a true thermal barrier that will reduce thermal loss in the header, reduce under hood temperatures, and make a fewhorsepower in the process, have your headers thermal coated by one of the many companies available or the headermanufacturer themselves. Most all of the coating companies offer inside and outside, multi-layer coating as standard. DO NOTallow your headers to only be coated on the outside, or just a single layer application! This is not a complete or qualityprocess. Some other considerations about the coatings. Once the header is coated, it is virtually permanent. That means that if youscrew up your coated header, it is not an easy job to repair and most header companies do not want to even attempt a repair.The coating permeates slightly into the header material which makes welding processes on a coated material less thanadequate. This is why you always coat the headers last, after all modifications to the header are made, and you are 100% surethe header will fit your vehicle. Lastly, an out of tune or tired engine can damage your header coating. A fuel mixture that is too rich or too lean can createhigher than normal EGT's that can and will damage the coating. Excess oil for a tired engine or assembly lube from a brandnew engine will raise the EGT's as the combustion process tries to burn off these items. Most header manufacturers state thatif you are installing coated headers on a newly built engine that you perform your initial break-in and tuning procedures with anold set of headers or exhaust manifolds before installing your coated headers.

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Exhaust Header Heat Wraps - Do Not Use

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