Old thread, coming back up.

Could you not just take a set of headers with only 1 oxygen bung and weld one into the middle primary, like the OEM manifolds? The problem I see with putting an 02 sensor south of an aftermarket cat is you need 02 extensions. I guess that's a small thing but another point of potential failure.

I only just realized the OEM manifold is steel and not cast iron.

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2001 E53 3.0 5pd