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Originally Posted by Blue XJ
Now that's an engineering answer if I ever heard one! But I agree 100%. The manifold design plays a role in it too, it's really only common on the trucks, the cars dont see stud failure as often. I assume the truck manifolds might be thicker in the mounting area not allowing them to expand/contract as much as the car manifolds.
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I doubt it's the mounting flange thickness as much as everything surrounding and attached to them, but maybe that's part of it too. The chassis mounts of the engine, the exhaust system, and the design of the exhaust system itself can all play a role. I imagine a unibody car has entirely different engine and exhaust mounts/isolators than a body-on-frame truck/SUV. The unibody car dampers are probably softer and more supple to mask more issues. This probably allows freer movement and puts less stresses back into the exhaust system and its mounts(the manifolds). The body-on-frame truck basically has an extra set of rubber isolators between the chassis and frame to ward off additional NVH issues from the occupants. 100% theory on that one, but makes sense in my head.