[dgc333]

If the pressure in the cylinder (boost x compression ratio) generates more force than the clamping force exerted by the head bolts the head will move. With typical aluminum head iron block engines the head bolts are torqued until the yeild (have been stretched beyond there elastic limit) to get an even clamping force. If you exceed the clamping force of the bolts they will stretch but will not recover, now your head is loose and in short order the head gasket will be blown.