Yeah, I think there had to be something funny going on with those bolts 3B used. They should have been far stronger than the manifold. Another point is that the bolt will also expand (lengthen) as it is heated, and even though the coefficients of expansion would be somewhat different between the manifold and the bolt, I can't see that an expanding manifold would be able to pop the head off a grade 8 bolt.
Hey, but then I don't know everything either.
Kurt
