if u look at a 2.9 manifold underneath, they are designed like this from factory, combined with a larger TB.. its just u cant ever find a 2.9 manifold for sell? this is just the same as that, vw did this only on 2.9s i believe?? my car is going 2.9 soon and has enlarged 2.9 TB already fitted, of course i will have to get a remap when all the mods are done..