This is definitely cool stuff. I didn't get to go through your posts well the first time. Thanks for putting in the research.
In the case of the e46 headers, the fact that they are lighter is not fully explained. Is it because they used thinner piping? or is it the weight of the aftermarket cats, maybe both?
The euro 330i headers are a cool design. I wonder if there are gains to be had by them. I would love to get my hands on a set. The flange at the ports looks exactly like the north american manifolds.
So now we have the following and correct me if I am wrong:
North American Headers for N52
- 323i & 328i & 128i Are the same
- 528i uses the same collector but different shaped piping afterwards
- z4 - unknown collector and piping specs
- x3 - unkown collector and piping specs
- x5 - unknown collector and piping specs
- 130i & 330i - Completely different collector