What is the consensus of opinion on this.
I'd heard that the Range Rover 3.9 manifolds were better flowing than the 3.5, but i would expect those on the SD1 car to be better.
What about the later 4.6 manifolds. I know these may not be cast, but i am trying to avoid using tubular which in my opinion can create a lot of engine bay noise.
I'd rather listen to the aural notes coming from the exhaust.
Which Cast Exhaust Manifolds
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for my money the SD1 4-2-1 are the best of the cast jobs but they don't fit a lot as they are long. That said the best of any of the factory manifolds is probably the 4.6. This is just a assumption on my part as I imagine as time has moved they would have made a good job of them. IRC they aren't cast though but stainless. JE Engineering used to do big bore cast manifolds. I don't know if they still do.