I was itching to mess around with my shops neighbors 2012 550xi. I hated what he had going on with his rear end so I'm slowly revising it with my own twist, even though he was against every idea, he's slowly loving the out come
Anyway... I ordered the F10 M5 diffuser from getbmwparts.com. Once it arrived, I had it painted AW, and went ahead to test if it... figured it would be a direct swap, I was wrong. In order to fit the M5 diffuser, it was either modify the stock tips and shift them a few inches, or pick up Quad Tips and get em installed.
Ordered Magnaflow Performance 3" tips and went ahead to install em.
Didn't get to far when I realized the tips are too long, and theres hardly any room to move the tips over a few inches to clear the diffuser, so... off went the mufflers... and up went my boner when I decided to test drive the car without them.
The amazing deep growl was too good to pass up on and some convincing was in order. After having the owner test drive it without mufflers on the way hom and back to work, he was more than convinced he wanted to keep the mufflers off and just add the quad tips.
I had the exhaust chopped about 2" before the mufflers, welded an extension pipe to a y-splitter, and finally attached the tips. I figured 3" tips would have been big enough, but now I believe a pair of 4" tips would fit nice and snug. Having 3" tips, I ended up adjusting them to sit closer to the top of the exhaust tip cut out, otherwise they looked just a tad too small from long distance.
But wait... theres more. Upon orderding the diffuser, I also tried sourcing the center insert which was impossible to find, I called half a dozen shops who specialize in BMW Parts import, as well as dozens of dealerships, and researched for hours and no one was able to obtain it.
Upon installing the diffuser, I also realized that I need to replace the plastic trim that goes over the rear bumper support/carrier, it's called an adapter for some reason.
The part numbers on the X and M models don't match.
xi: 51127299970
M5: 51127203976
So without trimming the stock bumper carrier adapter, the diffuser will not even go on. Since the owner had previously backed into an object and had slight damage that he had repaired, the adapter plate wasn't replaced, and I found that it was cracked. With that discovery, I went ahead and started chopping it up.
Some chopping up later, and the diffuser fit nice and snug, but now I was missing the mounting points for the fins that come down the side of the exhaust. How it works is the the diffuser is secured between the bumper carrier adapter and this center plate thats mounted to the floor of the trunk. I had diffuser which didn't fit the carrier adapter, and an adapter that was missing half the mounting points because it had to get chopped off to accommodate the M5 diffuser, and on top of all that I was still missing the diffuser center insert, which I'm 100% sure won't fit unless you completely remove the non-M5 bumper carrier adapter.
Diffuser fitted, with a preview of what the tips would look like...
Welding in progress
Then, I decided that once the F10 M5 parts become a little bit easily obtainable, I would order the bumper carrier adapter, along with the bottom center cover (which by the way doesn't have any part numbers or diagrams listed by RealOEM.com) and the diffuser insert for a complete OEM M5 diffuser revision.
I wanted to make a temporary diffuser insert using a spare M-Tech diffuser I had laying around, while digging through the pile of Infiniti/Nissan/BMW parts, I found a carbon fiber G37 diffuser I had laying around for several years from a prototype project. Without giving it second thought, I went and cut out a big enough piece to fit in place of the M5 diffuser insert, but not without a few hours of cutting, flipping, drilling, trimming, and suffering from the carbon fiber itch did I get it to fit almost perfect. The end result looked awesome. I had successfully secured the insert to the bumper carrier and to the underpanel center cover with the bottom ends of the diffuser sandwiched in between for a really sturdy and reliable fitment. At the end of the day, diffusers go through a lot of wind pressure, especially at high speed, so it's important to secure everything as tight as possible, whether it's heavy duty clips, or screws w/ bolts.
Upon completion, I painted the diffuser insert flat black using plastidip to prevent any chipping and to disguise the CF trim since nothing else on the car was CF.
Before the post gets too long, here are some pictures and a start up video of the exhaust. When I get a spare hour, I'll upload some videos and feedback on the muffler delete prior to adding the extension pipe, after, and overall sound and performance affect.
Till then, enjoy some of the pics. (VIDEO IS AT THE BOTTOM OF THE POST)
In the middle of it all, I felt compelled to rip the ACS trunk wing... unfortunately it was mounted using windshield polyeurethane, and removing it wasn't even a task, nor a pain in the ass, it was literally nightmare. It was well worth it though because I really wanted to throw on the AW performance trunk spoiler on it I had laying around the shop.
All done up
Carbon Fiber:
Flat Black:
Some cool instagram'd photos I had done during the process for social teasing.
VIDEO:
http://www.facebook.com/photo.php?v=339208362801392