This exhaust system has been one seriously exhausting undertaking. But, it is mostly done now (just need to weld the hangers on).
The biggest challenge was fitting this exhaust with cats and getting the x-pipe to cooperate. I had to section the DS front leg and kick it out, add a bunch of pipe sections, and grunt a lot. Holley got this right on their Blackheart exhaust. Speaking of Holley... I really don't think they were thinking about using full-sized cats with their headers.
I decided to put a second WBO2 bung in the x-pipe to get a balanced reading off both banks. There is some debate about how much error there is having a sensor post-cat (0.1-0.5 AFR on the gas scale) - however for the purposes of baseline tuning it is plenty accurate. I will move the sensor forward of the cat when I start doing WOT blasts.
Other than that it was just a bunch of tweaks to make sure the cats, pipes, mufflers, and tails were all even and level.
Back to tweaking the tune. I will post another idle video once I get the tune better sorted (and yes, it sounds sweet).