its pretty typical of cast iron turbo manifolds to crack, even factory ones where the turbos are often supported. However, your crack is coming at extremely low mileage, much earlier than I would say should be expected.
I dont know if I think supporting the turbos is the fix. I suspect it has more to do with the stresses of the part expanding differently in different locations based on the mass in that area, and the heat applied to it. I wonder if longer runner cast manifolds might go longer from having more space for expansion before the next "node" if you will. I am not familiar enough with different metallurgy to know if the same design would be more durable if it were thicker or higher quality casting. Perhaps making it thicker could make it worse?
I know that the greddy manifolds crack too. And factory turbo cars I work on often have cracked manifolds.
I am not defending a manifold cracking in 5000 miles though.
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