Our Fastruck driver was told...
Our Fastruck driver was told to pull the header wrap tight.
A gas at a higher temperature flows faster than one at a lower temperature because it has more energy. In an exhaust header, a higher flow rate can extract more leftover combustion waste and pull more fresh mixture into the combustion chamber. One way to increase the exhaust header heat is to wrap the header with a material designed to hold the heat in the pipe.
On our Fastruck project racer, we used header wrap on our DynaTek headers. These headers, by the way, are the crossover type. The left header crosses over the transmission and behind the distributor. The two sides come together at a "Y" on the right side of the transmission, and then a single pipe channels the exhaust out of the right side. We are required to run a muffler at some tracks, so we decided to make the DynaTek muffler a permanent part of the installation. DynaTek recommended this setup for our engine and the tracks where we run.
We extended the header wrapper all the way past the end of the muffler to get maximum effect of the wrap. This also keeps the area under the hood and beside the driver cooler. A more comfortable driver on a hot summer afternoon will be in better shape during the last part of the race. Kim Scheffler-Bennett, our Fastruck driver, was given the job of wrapping the Dynatek headers. She had little trouble with the stainless ties. She wrapped about two turns from the flange and then stopped to put on the stainless ties, which function like a plastic tie-just pull them tight and cut them off.
We were wrapping the header...
We were wrapping the header on our SCR Mini-Stock Honda. We found it would have been easier to remove the header. However, since we were this far, we decided to go ahead. It really was not that bad.
Our other project racer is the Honda Mini-Stock. This job was made more difficult by my being lazy, or at least I thought I was! On the Honda, the wrapping was done with the header on the car. We were looking for a performance advantage, but we were also trying to cool the oil. In many of these small front-wheel drive cars, the exhaust exits the engine at the front of the car. It then goes down and under the oil pan. Anytime the exhaust runs in close proximity to the oil pan, there will be heat transferred to it.
The header flange, when off the car, was clamped in a vise in a way that prevented it from interfering with the process. I don't recommend doing this job with the header in your lap. Kim had never done this job before. I gave her little instruction, simply telling her to "overlap it 1/4 inch and wrap it tight." You should start the wrapping about 1/4 inch from the flange to allow clearance for the header bolts. In one evening, she had wrapped the DEI (Design Engineering Incorporated) material onto both headers. She did a neat job of it, too. A pair of snips and a pair of pliers were the only tools needed for the job.
Our DynaTek headers were new. If yours are old, the use of a wire brush and a coat of high-heat paint, such as VHT, would be a good idea.
Starting with what seemed...
Starting with what seemed to be a long enough strip of the Thermo-Tec material, we wrapped down one pipe and up the next. We came up a little short. As the directions say, start at the header flange.
Wrapping the Honda header was a bit difficult because it was already on the car. I slipped the radiator off to gain access to the header. Using the Thermo-Tec wrap, I had my choice of a 1-inch-wide wrap or the 2-inch-wide material. Even though the pipes had a close bend at the header flange, I decided to go with the 2-inch wrap. That part posed no problem. I did have some trouble trying to keep the wrap in place while positioning the stainless steel tie and pulling it tight. I was working on my knees with the header on the car. To make it easier to hold everything in place temporarily, I used plastic tie-wraps on each pipe. This procedure also allowed me to stop in the middle of wrapping a tube, and it let me view the entire job. When I was satisfied with the job, I then used the stainless steel ties, placing them next to the plastic tie. Of course, you'll have to remove the plastic ties unless you like the smell of burnt polyethylene. The stainless ties work the same way as the plastic ties, but they don't have the elasticity that a plastic tie has. They only pull tight.
When wrapping an existing header installation, do not wrap over oily areas. Enclosing the oil can potentially cause a fire. In the Honda, I used non-flammable brake cleaner on the pipe surfaces under the engine before I wrapped the pipes. The Honda pipes were wrapped to the end of the collector, which was also the end of the exhaust system.Although I haven't been told, the wrap seems to be made of a Kevlar/fiberglass weave material. It is definitely resistant to the heat from a header pipe. Thermo-Tec says its header wrap was purposely designed to not over-insulate the exhaust system.
The shortfall can be fixed....
The shortfall can be fixed. Insert the patch under the original wrap. Finish the wrap and put a tie over the joint. You will see here that plastic ties have been used. These are placed temporarily to make sure everything is where you want it before applying the stainless steel ties.
One of the complaints I have heard over the years is that wrapping headers will cause them to burn out. I've just not had that experience. Yes, the wrap does hold more heat in the header tube. This is what makes more power. The proper way to wrap a header is to overlap the wraps by only a 1/4 inch. Too much overlap insulates the tube too much, causing a hot spot. It also uses too much wrap. As long as the wrap is properly done, with only a 1/4-inch overlap, there doesn't seem to be a burnout problem. The heat then seems to be evenly distributed across the header surface, which reduces hot spots in areas such as the outside of a bend. Remember that any header will eventually wear out. Most often, this will be the result of rust accumulating on the outside of the header.
Paint that allows the wraps to keep their appearance is now available. The paint also protects from oil absorption. Header wrap is available in two colors, black and tan. Thermo-Tec has a copper-impregnated wrap, giving it that same color. Plastic tie-wraps for temporary use help to make this a foolproof job. It is not difficult to wrap new headers before they have been installed. Headers that are already installed can be wrapped with a bit more care. Clean old headers with brake cleaner, a wire brush, and a coat of high-heat paint. Proper wrapping (1/4-inch overlap) promotes the right amount of heat insulation. Like they say when finishing the making of a movie, "That's a wrap."
The top section of the header...
The top section of the header is finished. Plastic ties hold everything temporarily.
The job is finished and the...
The job is finished and the permanent stainless ties are installed.
Kim carefully matches the...
Kim carefully matches the wraps to the necessary 1/4-inch overlap. Attention to this ensures longer header life.