This has been discussed extensively previously, but the condensed version is that mild steel will crystalize if it is unable to rid itself of the heat generated by the exhaust. The wrapping does an excellent job of retaining (not radiating) the heat in the pipes and at that point the pipes become an expendable commodity. In my build (see my gallery) I had areas on the driver side that I was quite concerned about (1/2" ) and after ceramic coating and reflective matting everything appears to be ok. The aluminized reflective matting does a very good job and at the same time provides an "Air Gap" to some degree. If I were to do it again I would make the headers out of 321 Stainless without the coating as stainless by nature retains more of the heat and radiates less.
Rick
