Might need to watch this stuff. The industry accepts that it will trap moisture and rot headers early, but the rumor is that it works like a blanket trapping heat around the headers and melting/cracking them. This info is still floating on the 'underside' of the performance scene, but I've seen it more and more. Including testimony from people said to have experienced it themselves. I used it for about a year and when I pulled it my manifolds WERE cracked, although this is hardly enough to prove the wrap did it. Meh, dunno.
BTW, rule of thumb I've seen before is 10-15* = 1% but thats just what the "internet" says.
Stuff got done.