Yes there is a reliability factor, unless your header is cast iron like stock then most will crack, over time stainless steel is thinner than iron and after all the heat is trapped the header will crack sooner or later, I use to be part of an integra forum and this is all what happend to their stainless steel and ceramic headers, people with the ceramic header also started having rust as the moisture is trapped under the wrap from rain or road debris, you are correct about the header handling the heat but your incorrect about the header holding the extra heat, the header was designed to be stable unwrapped, if you were to wrap the header that would be trapping the heat in the header ulimately leaving it to crack (stainless and ceramic) now if it's on cast iron because my inline pro turbo mani on my old car was cast iron it did make a difference, I could actually touch the manifold with the wrap after a hard drive with no problems but if it's stainless or ceramic forget it it's not worth the ceramic to "rust" and look like crap or the stainless to crack.

 

I had header wrap on my stainless DC header for my prelude for several years with no problem. Definitely reduces underhood temps, especially with stainless. I also should note, I live in Portland, OR, and this car was daily driven in rain 9 months out of the year. Like I said, I've had no problems with it.

 

If you are telling me that cast is more heat resistant than stainless and normal steel, I would have to disagree. Cast has lower specific heat and higher thermal conductivity and can take significantly lower levels of mechanical stress due to thermal expansion.
The bottom line is that if you have a piece of crap ceramic header then yes these things can happen, but I have never heard of stainless cracking.

I think your case is different as well. The fact that he is inquiring about a header wrap mandates that this is an NA application where temps are much lower, prob max at 1100 F or so. The only thing that I have not seen yet is a wrapped stainless turbo manifold, but that is a totally different ballgame since turbo temps can reach up to 1600 F.

http://www.matweb.com/search/DataSheet.asp...1ece120e4d563e0
http://www.matweb.com/search/DataSheet.asp...4ff365ed99b96f9

 

Stainless can crack under high heat. It might void the manafactures warranty if you wrap them.

 

Like I said you may not have problems right away but sooner or later the stainless will crack I guarantee it.