Discussed this issue yesterday with my tuner. Told me the same about Cosworth's. It was build in by Ford because of the resonation of the engine block at some high revs, which causes the turbine to move at least 5mm to 10mm; which is a major factor for manifolds to crack. He told me that his idea for my turbine setup is to make a bracket from the turbo flange to the block, and one from the down-pipe to the block (something like this), maybe some kind a damper to take weight away from the manifold. This would enable the manifold still to expand when hot, but sort the movement/resonation issue of the turbo. Did make sense to me 
rgds
habib
rgds
habib