QUICK_AG

Got the j's header, no strange noise here, LOVE it and it is a lot lighter than the stock header. I do not recommend wrapping your header EVER(holds moisture in and usually destroys the header-rust)! I am only using the one heatshield that bolts to the body by the battery and have had zero problems with heat.

Race Miata

It's more about risk cracking than rusting when wrapping a header unless you drive no more than a couple minutes a trip in the snow and then let condensation build overnite. I can't imagine the heat from the header will allow any moisture trapped by the wrap, especially on our FR car where the header is not right behind the radiator. Like I said I had my mild steel header in my miata for 100k miles and 7 years with no rust on the wrapped part.

Besides reducing noise and engine bay temperature, the main reason to wrap the header is to keep the heat in the header to increase scavenging effect. The time when I had no wrap with my miata header, I could see fuel mixture lean out (suggesting increased scavenging effect) after prolonged WOT resulting from header getting red hot.