Stock front exhaust pipes with mufflers weighs 12kg, the Y pipe came in a 13kg
I'm pleased with the result, at normal around town speeds the exhaust is quiet with a nice bass underneath it all
If I did this again I would go slightly smaller on the pipe , 75 to 80mm instead of 110mm, still sorting out a clearance issue, the LHS pipe is touching the LH transmission mount under hard acceleration. I have to make a clearance depression on the pipe a bit deeper (0.5cm at the moment, I'll try 1cm)
The 'butt dyno' says something good has happened, at 90kmh in 3rd gear the front of the 530i lifts noticeably when the accelerator is floored. Throttle response above 4,000rpm has improved.
The exhaust gas leaving the tailpipe at idle is a constant and steady stream , when I put my hand in front of the tailpipes I can't feel any gas pulses.
I did some calculations tonight and the Y pipe has 3 times the capacity of the front pipe it replaced.
Here's a short video taken in a not ideal place to try the exhaust out, lots of traffic around, speed humps etc. It does show you how quiet it is at low rpm. I didn't get above 3,500rpm
I took the 530i through a tunnel tonight at 6,000rpm and it sounded very nice.