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For your consideration is a Stahl Header for an R53 MCS. Has been on the car for ~20k miles and is very good condition. 1 5/8" stepped to 1 3/4" primaries into cone tapering to 3". The flange has been decked recently to insure it is flat. Includes Flex Joint. Does not include any gaskets.
New these sell for $1000 + Flex Joint. Asking $600 shipped in the US.
I'd imagine it will allow it to breathe better. Also being a long tube header it should move the torque closer to midrange. I've never tested it on a JCW but with it's better savaging ability of OEM I'm sure you will see some gain.