I planned on wrapping the entire exhaust system to keep the heat put of the engine compartment. You think thats a bad plan?

Bob Mears
Supermarine Spitfire

I tried the heat wrap idea on a set of .140 wall mild steel headers. It worked fine until I plugged up a main jet a bit and ran one housing lean. Of course the driver didn't notice the EGT go off the scale and the outside of the bend on the front tube came within a second or so of failing. After it cooled down, you could see a slumped shape at the bend. I felt it and it was soft. I crushed it with my hand.

 

After that I mounted a movie camera to watch the gages.

 

The thick walled mild steel works OK but you have to leave the bends (where its thin) exposed to airflow.

 

After that, I just wrapped the pipes beyond the collector and even the stainless muffler. I have just a blast tube (3") blowing on the bare header pipes and they have stood up just fine. With stainless you could wrap right up to the flange.

 

The pipes will loose close to nothing temperature wise under the wrap. You can hold onto the pipes with the engine running. So, the tubing selected must withstand the highest EGT you produce, and then a bit more as a safety margin. 

 

You can control EGT by staying well rich of peak for take off and climb, and then go quickly to well lean of peak EGT for cruise. Unfortunately, best power is just slightly rich of peak EGT, and that can be as high as

1,800 degrees. If the whole pipe is wrapped, then the whole system would be close to the peak temp.

 

You never want to spend more than a few seconds at peak because it overheats the center of the apex seal and will warp it if you keep doing it. Paul Yaw seems to go a bit higher with stock seals without ill effect.

Carbon seals wear quickly above 1650. Ceramic seals cost more than your house, but survive any temperature you can generate. And do not seem to wear at all.

 

My EGT probes are 3" out from the port face and on the outside of the bends (where the gas flow will be).

Per engine builder Daryl Drummond.

 

I wrap with 1/2 overlap so in effect there are two layers of material just about everywhere. The stuff is very stiff and hard to form. Soak it in water before you start, and pull it tight. It can be pulled into a slight bias on bends, and more overlap may be required to get two layers everywhere. Put on hose clamps as you go along.

 

Then use tight safety wire loops about every inch to hold it on. Remove the hose clamps and do another section. Most hot rod shops have it. Warm the engine several times going to higher coolant temps each time. Once the stuff is completely dry, full temp operation is OK. It does get kind of dry feeling and has very little strength once it has been to full temperature. You can wire stainless foil around it, in areas where you rubbing on it will flake it off.

 

In stainless or better material I see no problem with wrapping.

 

Indy car headers are about .020" thick Looks like razor blade material, and the collector and turbo are mounted with a bit of movement available. The pipes squirm around a bit at different temps and a bit of 

movement helps avoid stress cracks. So holding a long section tight at both ends may lead to trouble.

 

Mounts are generally a half tube cradle with the pipe held in place by a bit of strap held down by a short spring.

 

You can pull up on the pipes and they will move off of the cradle with ease. So they can lift up a bit due to heating, and can grow and shrink with no problem. For airplanes you could safety with a slightly loose loop of doubled wire through the spring, in case it fails. The pipe cannot escape and, the spring parts will be still on the wire. 

 

Just some thing to think about.  

 

Lynn E. Hanover