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Aftermarket Cat-Back Exhaust Installation Tutorial
Aftermarket Cat-Back Exhaust Installation Tutorial
including parts list and tools list -- no surprises!
Published by blndweasel
Default Aftermarket Cat-Back Exhaust Installation Tutorial

It's high time I contributed something useful to the forum, and this weekend I installed my Stroemung exhaust which I purchased from a fellow ORG member, so... here we go!

Things you'll need:


12mm 6pt. 3/8" drive socket (preferrably deep socket)
13mm 6pt. 3/8" drive socket
3/8" drive ratchet
3/8" drive breaker bar (with extension pipe if handy)
?22?mm box wrench for O2 sensor removal (double check measurement, I was using a 15" crescent wrench)
Tin Snips (optional)
Dremel rotary fiber cutting discs (or a real grinder if you have access to one)
WD-40 or other penetrating lube

Standard lift equipment (jack stands, wheel chocks, jack pad, jacks)

Parts (prices from Pelicanparts as of 3/21):

07119901575 Hex Bolt With Washer, M8x85-Z1-ZNS $1.00
11761716668 Compression Spring $2.75*
11621744323 Hex Nut, M8 Compression, Copper $4.50** See notes below
(sub: 11-62-1-711-954-M58) $.050
18211105635 Midpipe Rubber Hanger w/center divide $2.50
18211247422 Stock Exhaust Rubber Hanger (long) $2.25
18207535665-BOE Mini Rubber Exhaust Hanger (short) $8.25*** See below
Permatex Anti-Seize Lube $6.00

* When I priced out the OEM exhaust hardware, this M8 nut came up as a non-returnable $4.50 ea. item. I was like "whoa" in my best keanu voice. Or maybe it was Joey Lawrence. Whatever it was, it was in a distinctly mocking tone. Use the substitute part, which is absolutely the same thing, priced at $0.50 ea.

** You can re-use your existing compression springs if you prefer. I ordered some just in case.

*** These Mini Rubber exhaust hangers are useful on the Stroemung, as noted in previous forum posts, as they tuck the exhaust up a little better under the car. Plus they're really stout compared to the stock BMW unit.

Here we go:

1. Lift the vehicle for adequate access to the undercarriage (min 12-18" depending on your ummm... girth)

Now if you're a smarmy tool-whore like I am, you've got one of these: a jack pad (~$30 from pelican) which conveniently fits in the cradle of your 3-ton floor jack. No risk of damaging the underbody with improper jack placement. Also makes it much easier to position jack stands once the vehicle is in the air.

Be sure when positioning forward jack stands to find something solid to perch them under. There are lots of areas down here that seem like they would be sturdy (i.e. floor panels) that will easily deform once the weight of the vehicle is resting on it. Personally, I place my jack stands just outward from the frame junctions where the undercarriage x-brace mounts up (pretty much directly beneath the motor mounts).

If you are jacking the rear of the vehicle up first, you'll want a set of wheel chocks. Now these are fancy aircraft chocks, but you can accomplish the exact same thing with a piece of 4x4 lumber ripped at a 45 deg angle in a mitre. You can build a set of these from Home depot for under $15... hmmm... I'm picturing fancy painted wheel chocks with 318ti.org logos stenciled on... perhaps for car shows?

It's well worth it to pull at least the driver's side rear wheel off, as this will allow you to move the exhaust in and out from under the vehicle without too much trouble.

2. Once you have the vehicle hoisted, it's time to address the exhaust flange bolts. Chances are, if your car has ever lived somewhere where they salt the roads, these bolts will be rusted to hell. Expect to have to cut the old bolts off. To do this, you'll first want to remove the cat-back O2 sensor which can be seen in this picture:

I didn't have a box wrench on hand that was large enough, so I used my 15" crescent. I'm guessing it's a 22mm fitting. Before loosening the sensor, be sure to first remove the molding that protects the wiring lead, then disconnect the O2 sensor at the plug just forward of the cat. This way, when you unscrew the sensor, you won't twist the wires.

3. My suggestion next is to grab a 6-pt 12mm deep socket driver if you have one available. slip this over the threaded end of the exhaust flange bolt, to reach the flange nut. If you can secure a good hold here, you can save yourself from doing any cutting. Be sure to only use a 6-point socket, as a 12-point socket will probably just round the nut off.

If the deep socket 12mm 6pt fits, you're good, if not, proceed to cut the threaded end of the bolt off:

I didn't have the luxury of electricity, so I used some fiber-wheels from my dremel, with my 9V cordless drill. I went through 5 cutting wheels and two fully charged batteries! (i.e. remember to charge your batteries the night before)

Now, liberally spray the area with penetrating lube. Let it soak in for a few minutes.

Secure your 12mm 6pt socket to this nut, and the 13mm 6pt socket to the bolt on the other side. Snap your 3/8" drive ratchet to the bolt side, and snap your 3/8" breaker to the nut side. Turn the ratchet in the loosening direction (remember, "righty tighty, lefty loosey") and your breaker will begin to move towards the passenger side. Let it rest against the body / heat shielding to provide resistance. If you don't have a breaker, you can use a second drive ratchet here instead. Set it to "lock" if you can.

Now that you have some resistance on one end of the fastener, it's easiest to use a pipe extension on your free ratchet to bust the fastener loose. If you don't loosen the nut, you'll just snap the bolt. Either way, you've just finished the hardest part of the job!

3. Support the exhaust system with a jack just under the forward portion of the muffler. (Your vehicle should be on jack stands at this point, so your jack should be available)

4. Cut the exhaust hangers. Believe me, don't try and remove them, it's not worth the trouble. Cut them and replace them with new ones. It's easiest to use a pair of tin-snips here, but if you don't have a set, you can use a hacksaw, or even just a pocket knife. The hangers should be rubber with some light integrated reinforcement threading, easy stuff to cut through.

Once you cut the last piece, the exhaust should be resting on the jack.

5. Position yourself under the exhaust, next to the jack, and slide the exhaust off the jack and onto your body... it's kinda heavy (35lbs) so beware, if you're a total wuss.

6. Prepare the new center exhaust hanger before installing the new exhaust. Note in my photo here that the old center exhaust hanger didn't have a divider in the middle. I'm sure this was causing squeaking, as the exhaust mount tab and the frame exhaust hanger were rubbing (evidenced by lots of rusty dust in the area) The correct OEM hanger should look like two capital letter "D"'s stacked against the flat edges of one another.


Note, the second photo is what things will look like *after* you install the new exhaust... read on...

8. If you're installing a Stroemung and it doesn't have a sub-frame clearance provision, now is the time to hammer it into place. I used a stack of towels to set under the pipe, and I protected the rest of the exhaust with towels so that it didn't get scratched up while I was wailing away at the pipe. I used a 10lb mallet and just went to town on the thing. Left a few marks, but overall it was relatively clean, and since it's not in a noticable spot, I didn't really care. Just try to avoid hitting the pipe at an angle, or you'll leave gouges from the edge of the mallet face.

If you don't know where to make this provision, it's just aft of the second bend in the midpipe, going back from the cat flange. Start immediately after the bend, and extend the depression about 3" back from there. If unsure, do a test fit, or compare your new exhaust side-by-side with the OEM unit.

You don't have to hit the pipe... erm... dent the pipe a whole lot, that is, just enough to take 1/4" or 1/2" or so off the outer diameter. Don't overdo it, there's no reason to.

9. Prepare the exhaust flange at the cat with some exhaust assembly paste, or if you don't have that, you can use anti-seize lube if it's rated to a high temperature (e.g. Permatex #80078, available at pep-boys for $6 / 8fl.oz. look on the bottom shelf)

10. Prepare the jack now at a slightly lower position, and cover the lift cradle with cardboard and preferrably some cloth (so you don't scratch that shiny new exhaust!). If you're smart, you'll also tape the cardboard and cloth down so it doesn't slip out of place while you're under the car.

Next, positioning your body under the exhaust, lift it up onto the jack, while also positioning the forward most exhaust tab (mid pipe on new exhaust) to properly slip into the matching hanger on the frame. At the same time, you want to aim the exhaust flange to mate properly with the cat. The exhaust flange might not set up properly at this point, so just make sure the exhaust is supported well by the jack and that you mate the center exhaust hanger. That gives it two support points, and you can just balance it for now.

11. At this point the exhaust should be loosely supported under the car without your help. Now install your new exhaust flange hardware and torque to factory specs (I just guesstimated at around 40 ft. lbs, but I have lots of experience with that sort of stuff... be careful, don't snap those bolts!)

Reinstall the O2 sensor while you're down here. Follow OEM torque specs. If you're a "pro", you can guess like I did. Don't forget the wire molding cover!

12. Now you can finish up with the rear exhaust hangers.

Mini hangers such as these will raise the exhaust assy. by approx 1/2" or so. Plus I think they're far more stout than the stock hangers. Install the hanger on the frame tab first, then slip it onto the exhaust tab.

13. While the car is still on stands, start the engine up to listen for leaks. If all looks good, then you're set!

14. If you removed your wheel, make sure to check your lug torques once the vehicle is off the stands.

Unfortunately I don't have any pictures of the finished product! I was wayyyy too stoked to hear that my mysterious exhaust vibration at 2500 RPM was apparently coming from the resonator in the midpipe. No more noise! It wasn't the cat afterall! All I could think about was going for a drive at that point, so hence the lack of photos.

The exhaust tip is a little close to the left side of the opening in my sport bumper. I suspect that if you tried different combinations of Mini hangers and OEM hangers, you could center it a bit better than I did. It wasn't rubbing, so I didn't care too much.

A little less than an hour into my celebratory drive, I was stopped by a fellow in an M3 who wanted to give me props on the Ti. Mannn... that certainly felt good : )

Hope this helps


the blonde weasel
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By thesk8nmidget on 03-24-2008, 10:39 PM

nice write up!!

good pictures!
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By ATF on 06-12-2008, 05:12 PM

Awesome write up, I had a quick question. What exactly is exhaust assembly paste? I stopped by AutoZone and noticed they had several different pastes. I think one was a repair kit, and probably isn't what I want. What does the exhaust paste do? Prevent exhaust leaks or is it simply anti-seize type lubricant?

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By E36 Typ-M on 01-23-2010, 07:50 AM
Default 318ti exhaust

Do you think its possible to relocate the exhaust more to left becuase I want to install an M-Diffuser?
Can you please help me thank you
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