M5 Expert (>4000)
Join Date: Oct 2010
Location: Cobourg Ont
Thanked 1,967 Times in 1,651 Posts
I am not the first to have done this but likely have the most development time into it. I never did do a full thread on this but have replied in other posts with pics and details. Worth your search in the E39 M5 specific forum. As far as how it works, better than stock and many of the faults are removed. Other than welding fittings to the double walled header pipe all the rest of the tasks are easy, drill holes and use compression fittings. This is a real fix as the system works as designed and is likely why BMW has gone this route also.
It is so much easier than clearing the head passages they can't be compared. Heads cost is $10,000, reworking the system (once I had the design and some fabricated parts) took one evening in the shop. IIRC the total for the parts was less than $300. The design took a very long time because I had to do many experiments.
I have made some suggestions on how to do it now, learning from what I have done and I suspect that path would be 3 hrs work, no fabrication work, and $150 for parts plus wielding 2 fittings to the exhaust.
It is easy to just code it out, but the system working offers some advantages that are worth while. It is only easier to code it out if you can do the coding yourself or use one simple tool available. Otherwise coding it out using a tuner costs some big bucks as they seem to only offer it bundled with other mods.