I do not recomend wraping the headers not only on turbo cars but any header. yes it holds the heat in, and keeps it there. The Idea behind it is to keep the exhaust gasses hot longer for a faster flow, and on a turbo helps the turbo spool a little faster, or that is the idea anyways. I noticed absolutley no difference on spool time in my car vs wrapped or not. But that heat that is held in litterally cooks the header, Mild steel is worse but it will do the same to stainless, it actually crystilizes the metal making it very very brittle and weak. The end result is a header that is very prone to cracking at welds and just exhaust gasses litterally blowing thru the header on bends. I know this first hand as it did it to my headers.

Scott do not wrap your turbo headers unless you like building them.

Steve