Appreciate all the feedback/updates, looks like this header is a no-go.
Might be getting off-topic now but has anyone else noticed that all S54 header designs have unequal length secondaries (the pipe following the 3-1 merge)? Perhaps addressing this and equalizing the lengths in section 1 before the X-pipe crossover will clean up the sound.
Kind of similar to what the S55 guys are doing.
https://f80.bimmerpost.com/forums/sh....php?t=1675268
I have been looking at V6 engines that sound nice and one thing I find in common is equal length per bank. Obviously this is a lot easier to do on a V6 than I6, hence maybe BMW left that out when they designed the exhaust.