I'd tried the part they're now calling the Tru-X Crossover on my 4.4 in place of the center resonator a couple years back. It completely destroyed all my midrange torque. So much so that in places I could comfortably pull my race car trailer in 6th, I struggled to pull in 5th. And at 65 on the interstate I couldn't pull hills in 5th gear like I used to. I had my local custom muffler shop pull it off and he custom made a new pair of pipes with a simple crossover balance pipe between the tailpipes and voila, all my torque was back.

Exhaust work is a science and proper placement of an x-pipe is probably critical. Maybe if I'd moved my x-pipe forward or back a few inches it might have helped but I wasn't about to go any further. And FWIW, I've tried the x-pipe assembly on another 4.4 and he had the same problem. But when we tried it on a 3.0 it seemed to work nicely but his wife didn't like the noise. So it's back in my basement again. A complete waste of $350 in parts and labor for my purpose unfortunately.

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'04 E53, 4.4 Sport
'97 E39 528i
'86 911 Carrera, track car
'96 BMW R1100R