They can still crack but far less likely to as Mild Steel is much less susceptible to big variations of expansion during a heat cycle than Stainless Steel. Mind you, most Stainless Steel manifolds are thicker in gauge than the equivalent Mild Steel ones whihc has something to do with it...
And heat wrap...that's fairly wrong, as in most cases, it'll help a manifold crack, not only by trapping moisture and bringing the onset of corrosion, but also by maintaining more heat within the manifold, for greater thermal expansion
Unlike most cars it is more expensive to make a mild steel because of the tight bends blah blah ect. Ivans used to go for around the £300 mark.
You can get a way with a silk road mani if you use trd engine mounts and a torque dampner and braced cat or decat.
@ timmy you can have all the engine bracing you like and the silk road mani will still crack, ask kuk-grant and a couple of others.
@ben-ep82 there is no mild steel mani left at the mo as every one has stopped making them. SPEEDVISION is a trader on the old site and shall be coming over to the new one shortly, and he has some mild steel ones in development, it should only be another couple of months till there available.
Main one is thermal shock or brittleness caused by rapid heating and cooling cycles, Theoretically speaking wrapping a manifold would make it less pron to cracking as it allows the manifold to cool slower therefore retaining the elastic properties of the steel, Moister can be solved by buying a paste that is painted on and seals the Wrap form moister,
corrosion isn't really a factor as it won't effect the manifold enough to cause failure without significant damage.
As for manifolds available, Sasha from WEPR has some new Evo Manifolds available but they require Modification of the turbo lines and a smaller radiator
Not really, Mild Steel is physically easier to weld than Stainless steel...if I went to my materials lectures I could tell you why, I just know it's got to do with the smaller quantity of Carbon in Mild Steel