MichaelDelaney on Feb/17/05 said:
stainless steel depending on the grade used is in itself a good insulator and emits less heat than say mild steel.
on non-stainless steel headers or low grade stainless steel, the problem with header wrap is that the heat cannot escape off the outside surface and stays there. The heat comes from the lumen of the pipe and conducts from the inside surface to the outside surface of the header but then it just stays there at that outer layer.This causes a heat sink at that outside layer or surface. Usually if the welds are of poor quality or if the steel is crap, you'll get cracking over time at the surface or at the welds from this "heat sinking".
In quality stainless steel headers, the heat is insulated both on the inside surface and the outside surface. So there's less conduction to the surface of heat and also no heat sinking.
The thing to ask yourself is this:
does it make a difference?
Let's say for the sake of discussion that the header does emit heat.
Does it emit heat enough into the engine bay WHEN THE CAR IS MOVING though?
And even if it does emit heat that raises underhood temp, does the temp go up enough to affect your intake temp. And does the "supposed" increased intake temp reduce performance (not hp...et or laptime) ?
From what we know, the "cold air" effect is hyped. When neouser measured the under hood temps in his Teg while he was driving around town and on the highway, the temp difference to the air outside was negligible.
Ok so let's also for the sake of discussion say that the underhood temps skyrocket and makes you lose 2 tenths off your time and you have to insulate.
The best way to insulate is not cheap header wrap. The best way to insulate is to thermal coat BOTH the inside of the header AND the outside. You'll find that coating is pretty affordable and not as expensive as you may think and is better than the wrap with all the claimed pluses or benefits of the wrap and better. It's the proper way to do it. (try hpc's or jet hot's websites)
When people spend $600-1300 on a hybrid header, they usually coat them. They don't header wrap them if they know the consequences of using header wrap.
You don't have to be spending that much money on a header to realize the down side of wrap. You get the header that you can afford and works well enough for your package's goals. You worked hard to get enough cash to pay for the header. Why would you then throw that away over cheap wrap and for what reason? Hype about under hood temp ?
