Exhaust manifold heat: wrap or heat shield?

An owner with a Tullet 4-1 found the boot area had become "like a turkey roaster" and asked whether wrapping the manifold would help. The thread gave two camps, plus a few cautions. Owners differ on which is better, and the answers below are their experience, not tests.

Option 1: better heat shielding

• One owner says to fit better quality heat shielding to the engine side of the boot bulkhead. The original shield is liable to melt with a stainless manifold. He fitted Nimbus about five years earlier, after the original melted, and says there is negligible heat in the boot, even with a supercharger and a 3" Tullet system. He also removed the foam pad with the heat shield coating from under the boot carpet (which freed an inch, and a crash helmet now fits).
• Another owner votes for Nimbus too. A third warns about the original foam: it came adrift on his car, touched the exposed manifold and caught fire, and nearly burned the car on a dyno.
• How he fitted Nimbus: two or three holes in the rear clam for bolts, a small air gap between the Nimbus and the boot wall (using washers if needed). It was no hotter than before despite an exposed Tullet manifold. Adhesive reflective insulation on the boot wall before the Nimbus is a further option.
• One owner left the original manifold heat shield off during a manifold swap and put Nimbus on the underside of the boot instead. Another says it is easy enough to make a Nimbus shield that fits where the original one attaches and covers the top and back of the manifold.

Option 2: wrap the manifold

• One owner says he prefers exhaust wrap wherever possible. His reasons: it keeps the heat in the pipework, so engine bay temperatures stay down; it doesn't rattle; it doesn't bend or break. Critical hot parts like manifolds can be double-wrapped. He has used wrap for at least five years and needs no other heat shielding round the turbo or manifold, and he removed the chimney above the manifold and brackets around the engine mount shields.
• His argument against Nimbus is that it only reflects heat that has already escaped.
• Another owner says stainless manifolds are wrapped to keep the heat inside, giving a higher flow speed. He never felt a difference in spool-up, whether wrapped or not, but says wrapping is good when you don't want to melt things or need to put your hand in a hot engine bay. He would wrap an aftermarket manifold. Cast manifolds hold heat anyway because they have more mass.

How owners wrap

• Damp the wrap first so it is more flexible and easier to apply.
• Overlap by about 50%, giving two layers.
• Use plenty of stainless cable ties.
• If you spray the wrap afterwards, wear a proper respirator: one owner wore a mask suited to 2K paint and could still smell the solvents. The spray made the wrap last longer.

Cautions

• The heat goes somewhere else. One owner warns that wrapping the manifold or exhaust can cause heat problems further down the system.
• Wet wrap steams. An owner whose car lives out in the rain says the wrap soaks up water and steams when hot, so much that four people stopped him to say his car was on fire. He also worries about wet wrap held against the metal shortening the manifold's life. That is his concern, not a measured result.
• It may not fit. A wrapped Tullet pushed on the water pump pipe on one car and caused a leak, so the wrap had to come off. See NA exhaust manifold replacement.
• Hotter exhaust valves? The original poster wondered whether a wrapped manifold would make the exhaust valves run hotter, and whether the one remaining cat would work better with more heat. Nobody answered either question.
• Check for leaks first. One owner asked whether the car has a cat, and suggested checking the lambda sensor and manifold for leaks.

For the plastic shroud above the tailpipe, see Exhaust shroud (heat shield) replacement.