5B1202 – BMW N54 Catted Downpipes

335i 2007-2010

335is 2010-2013

135i 2008-2010

1M 2011-2012

Congratulations on your purchase of the COBB Tuning N54 BMW Catted Downpieps! The following instructions will assist you through the installation process. Please read them BEFORE beginning the install to familiarize yourself with the steps and tools needed. If you feel you cannot properly perform this installation, we HIGHLY recommend you take the vehicle to a qualified and experienced automotive technician.

IMPORTANT! Installing this kit will require custom tuning or utilizing an appropriate Stage Power Package map if you have a matching mechanical configuration. Please consult with COBB or an authorized ProTuner in your area if you have any questions!

Parts List

Front Downpipe
Rear Downpipe
2 Gaskets
4 M8x1.25 30mm long Bolts
4 M8 x 1.25 Hex Nuts

Tools Needed

Phillips head screwdriver
Flathead screwdriver
3/8" ratchet
3/8" 8mm socket
3/8" E10 inverted Torx
3/8" E12 inverted Torx
3/8" E18 inverted Torx
3/8" 12" extension
3/8" 6" extension
3/8" Socket Swivel
16mm combination wrench
Oxygen Sensor Wrench

Removal of Stock Downpipes

Start off by getting the vehicle up on a lift or placing jack stands under the front of the vehicle in order to get it up in the air and give you some room to work. Make sure the emergency brake is set firmly and that you've blocked the rear wheels if you're using jack stands.
Loosen and remove the stock exhaust, The downpipe installation can be accomplished by just loosening the stock exhaust but it is much easier if the exhaust is removed. If you have an aftermarket exhaust, just the front portion would need to be removed. The exhaust bracket can be removed easily with an E10 Torx socket along with a 13mm wrench/socket. You will also need a 12mm socket to remove it from the 4 x DP Flange Bolts.
Next remove the front underbody panel using an 8mm socket. There should be 19 bolts as well as two into the subframe on the 1 Series vehicles.
Unbolt the steering rack using a 16mm wrench and an E12 Torx socket. The 16mm nut is hidden on the top side of the steering rack. Next lower and slide the steering rack over to the driver side to allow more space to access the downpipes.
NOTE: This may cause a Check Engine Light when you start up which will need to be resolved by having the dealership reset the steering rack position
Remove the steering rack heat shield using the T25 Torx socket. There are three screws that will need to be removed.
Before removing the upstream oxygen sensors it is recommended that you mark them in order to remember which ones goes in the front or rear pipe. This is critical as getting them mixed up will result in a check engine light and can potentially cause damage to your vehicle's engine. Once they are marked you can remove the upstream sensor for the front pipe using a oxygen sensor wrench or 22mm box end wrench. Once marked and removed do the same for the upstream sensor for the rear pipe.
CAUTION: Handle the oxygen sensors with care. They can be damaged easily and will cause error codes if damaged
Using the 12mm socket remove the two bolts holding the stock downpipes to the downpipe bracket.
Unplug the rear oxygen sensors and loosen the wires from the clips. Using one or two small flat head screwdrivers will help you to release the tabs that lock the sensors in to their connectors.
Next loosen the b-band clamps on both downpipes using the 13mm socket. Use a screwdriver if necessary to break the v-band clamps loose after the bolts have been removed.
Now you can go ahead and remove the front downpipe by first snaking it past the subframe.
With the front downpipe removed, you will now have enough space to remove the rear downpipe.
Remove the downpipe bracket with the E18 Torx socket (14mm will sometimes work as well). The transmission bolts are aluminum so be careful not to over torque on removal or reinstallation later.
Remove the rear oxygen sensors with a 22mm or 7/8” wrench.
CAUTION: Handle the oxygen sensors with care. They can be damaged easily and will cause error codes.

Installing the COBB High Flow Downpipes

Install the downstream oxygen sensors into the COBB Downpipes. It's recommended to put a bit of anti seize on the threads (being careful not to get any on the tip) so that they are more easily removed later.
CAUTION: Handle oxygen sensors with care. They can be damaged easily and will cause error codes. The oxygen sensor with a BLACK wire is for the FRONT DOWNPIPE and the oxygen sensor with a GRAY wire is for the REAR DOWNPIPE. Switching the front and rear oxygen sensors will cause error codes as will switching the upstream and downstream ones.
Install the rear downpipe by snaking it in between the subframe and the chassis. Secure the downpipe loosely into the v-band clamp using the 13mm socket but don't fully tighten it at this time
Install the front downpipe next. Again snake the downpipe between the subframe, rear downpipe and chassis to install. Secure it with the v-band but again don't tighten it down all the way.
Plug in the rear oxygen sensor cables. Make sure to double check the oxygen sensor wires and that they are installed into the correct downpipe.
re-install the mid pipe (or entire exhaust) to the downpipes using the supplied bolts, nuts and gaskets.
Once the exhaust is all lined up and tightened down, you can tighten up the v-band clamps on the turbo using a 13mm socket.
Install the rear downpipe upstream oxygen sensor first. Then install the one for the front pipe. This order is important as you won't be able to torque down the rear oxygen sensor when the front one is in place.
At this point you should be good to button everything back up using the reverse removal order. Once you have the rack hooked back up it would be a good time to turn the car on to check for leaks so you don't have to take quite everything back off again.