What is crystallisation and what does this do to the exhaust system? I haven't seen any engines with the intake wrapped but I've seen a alot with there exhausts wrap. Crystallisation is the forming of crystals. OK, doesn't really tell you much eh? I'll try to explain with my limited chemical knowledge until someone else can come in with a better explanation ... Any material will reach melting point if you apply sufficient heat. After this, as it cools back down the basic molecular structure can be alterered because both air and water, among other things, may ingress into the material while it was in a molten state. Also, the material used may be a combination of many base materials, an alloy in simple terms. Each of the separate base materials will have a different melting point so as the cooling occurs the individual base materials may re-solidify at different temperatures thus causing partial separation of those materials into their unique selves - destroying the qualities of the original alloy mix. So, as it cools it can crystallise and therefore lose some or even most of it's original properties and molecular integrity. Basically, with what we are talking about here, your exhaust system, the steel breaks down and can perforate or crack. Jeff,Well put mate , even I have got it now. :banghead: