Hi Guys - so many people have asked about this mod. I thought I would throw together a little DIY on my install. The main benefit of deleting the N54's secondary cats is more flow, better faster spool up of the turbos, and a louder more deeper tone of the exhaust note. I really like the way the exhaust note has changed. As far as power goes... its hard to say. I suppose deleting the secondary cats is good for a few HP on the top end. I know when I go WOT... the exhaust now has some BARK to go with all its grunt.
The the response time from off boost to on boost - seems better now. Throttle response feels slightly sharper.
N55 mid pipe
BMW part number: #18307599743
current price is around ~$333 for the mid pipe thru Tischer BMW
or United BMW
, or the like. I paid 330 euros over a year ago. So its way cheaper now as you can see. Back then the mid pipes were selling for over $420.
I would also HIGHLY recommend you to buy these parts...
two new front mid pipe gaskets #18307553603
new copper hex nuts 4
(my old ones were really rusted) for the front gasket. I am not 100% sure of this part number since my dealer had a hard time figuring out what size copper nuts my car used. Ask your dealer to be sure!
new rear exhaust gasket ring #18117553130
I also bought new springs and collar bolts for the rear muffler section, but I did not need to use them. The reason I bought them is I read some posts here that when removing the rear muffler, these bolts and springs tend to break. I did not want to be caught without these parts. They weren't that expensive, so I also bought them.
Spiral spring #18307790610
Hex screw/bolt with collar #18307561670
You will need a 13mm deep 1/2 inch or 3/8th's socket/ratchet for the front down pipe gasket nuts.
You will also need a rather large E-socket (reverse torx bit), I think it was an E18 socket. ? You should have a LARGE breaker bar... because you need to remove the X-brace under the rear exhaust/mid pipe area. This was the hardest part of the swap. It really wasn't hard using a lift and using air tools. I think I also used an 18mm 1/2 socket on the X-brace.
I would also have one hand some 3M scotch pad to clean up the old down pipe and rear exhaust bevel. Also having some WD40 or liquid wrench would help as well. ALWAYS use new fasteners. You can see my old DP gaskets... they were only on my car for about a year... and they just fell apart when I removed them.
I found out that the mid pipe nuts need to be torqued to 21Nm
or about 15 ft/lbs
. Also the same value for the rear muffler section to mid pipe bolts/springs. So keep that in mind not to over torque your new hardware(nuts).
Here are my pics of my install...
N54 on top, N55 mids bottom...
and some videos....
My car is totally stock except for a DME re-flash from... MS Tuning.de 380 PS and 520Nm
While the N55 mid pipe does make more mid range and high end power(were talking just a few HP) I did feel that I lost some low end grunt under 3K. Especially in the 1,500 to 3K range. A few months after installing the N55 mids I switched back to N54 mids when I installed a BMW Performance Exhaust. See the later pages in this thread for my thoughts on the PE.
before... N54 mids...
after... N55 mids...