If they're running it hard enough to shake it apart then they're running it hard enough to NEED parts replaced frequently. I always torque my stuff to the upper end of the torque specs and never had a problem.

 

vibration is the last thing that will cause an exhaust manifold to crack, more like cheap casting and bad design, my exhaust housing on my turbo on my talon is cracked, along with the manifold, it still had its balance shafts, exsessive heat or rapid temp. change usually is the culprit when cast iron cracks, the 420a DOHC in the neon ALWAYS crack the manifold because its a piece of **** design, the SOHC however never cracks it, yet its the same "buzzy" bottom end with a different head and manifolds , so where does that come into play with vibration
that is stress from heat expansion, not vibration

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not to bring up an old post, but since i had an attitude and just took the belt off the BS so it wouldnt be there to break and cause me more problems with my timing belts, i have LESS vibration, - YES it was in time, my car is 10x smoother without that heap of **** spinning around in the block