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Subject: Full Muffler Writeup with pics Author: rhett : member since March, 2005 : 1455 posts Posted on: 2005-10-15 16:57:20

Well, here is the full writeup from start to finish. Some of the pics are duplicates, but I wanted to include everything all in one posting.

Links to previous posts are at the end of this writeup

Tools I used for this:
1) safety glasses
2) Grinder - I used 4-1/2" grinder and 3 wheels all together
3) Sawzall
4) 10mm & 13mm sockets, 12" min extension
5) Large prybar and hammer
6) Torch Set
7) Welder - I used my Mig welder with 308L wire and Trimix Gas

First things first, remove your exhaust from your car. Make sure you soak the nuts/studs at the front with a good penetrating lube - I broke 3 out of the 4 on my car even though I did. If I remember right, they are 13mm nuts. Remove the black plastic covers that hold your rear O2 sensor connectors (10mm) and disconnect the sensors - no need to remove them. I would recommend placing jack stands under the exhaust pipes back by the axles and up by the rear cats. Next, remove the rest of the mounts for the exhaust - they are all 13mm. You will have the 4 bolts in the middle of the car, 4 nuts right behind the axle (this will remove the rubber isolator too), and the 2 nuts that clamp on the outside of each muffler. Now your exhaust should be free and resting on jackstands, the ground, or you depending on how you get it out. After its out, remove the rubber isolator mounts from the muffler hangers (10mm nuts x 2 each)



Step 2: Start Grinding the edges of the rolled lip all the way around the mufflers. You will also notice the hanger that is welding to the muffler towards the front - grind the weld away from the top of the muffler shell. When you are grinding, you will start to see cracks developing in your grind marks, since the muffler shells are dual layers top and bottom, you want to grind until you see 2 distinct splits in the material. You will also need to grind the weld away from the turndown on the top half of the muffler and at the ends of the seams.





Step 3:
Start to pry up on the shell if need be, if you ground enough material off the shell should be loose - don't plan on it coming off without some elbow grease. Grind extra material off where its not loose yet. I had the hardest time grinding enough of the turndown weld off.




Step 4:
Now you need to cut the internals away from the muffler. This requires 2 cuts - I used a sawzall for a clean cut. I saved about 2" of inlet pipe and outlet pipe originally. I then decided to put the tips on so I ground the turndown weld completely away from the lower shell (no pic).







Step 5:
Now that you have the internals of the mufflers out, you can either weld it back together and leave it empty, or you can make new internals for it. I chose the latter of course. In order to reuse one of the perforated tubes, you need to be able to grind the weld that hold it into the partition. In order to get clearance to grind the welds, I used a torch and cut both partitions around the tube. Then you can clamp the tube in a vise, grind the welds, and smack with a hammer and remove the partitions.




Step 6:
Here is where it gets a little time consuming. I ended up using a 12" section of 2.25" od raw tubing and the perf tube to make the new internals. You will need to grind/cut the proper angles on each tube and the internal inlet pipe in order for the pipe to come out the center of the muffler. Its a pain at first, but after a little bit of grinding, test fitting, and repeating many times you will get a good fit. After you have the perf tube and your raw tube fitting good, tack them together and cut off the excess raw tube. I then welded the 2 together and then welded to the inlet pipe of the muffler. My tips are 2-1/4" ID so they fit perfect on the new internals and in the outlet area of the muffler (wasn't planned, just got lucky thankfully).

I didn't take any pictures from here on out till the end so bear with me...

Step 7
At this point, leave the tip in place and clamp the top shell onto the lower shell - a couple pair of large vice grips work nicely. Tack the shells together every couple inches. DO NOT TACK/WELD THE TIP ONTO THE MUFFLER YET - it will need to be tacked on in place in the car. Weld the seams together now and the front hanger to the upper shell lip. One thing to not hear, make sure and clean the shells as best you can before you weld. Wirebrush, brake cleaner, compressed air - anything you can use. I was fighting my welder the whole time because I didn't prep the metal before I welded.



Step 8:
Re-install the exhaust at this time without the top shell on. You will need to decide how to cut the fascia so it matches the tips profile and also need to lower the mufflers. I cut the fascia first, then lowered the mufflers. I screwed up and didn't match the profile of my tips, my cut ended up more rectanglish with small corner radiuses instead of larger radiuses that matched the tips profile....Remember measure twice or more, cut once.
Since my tips are 3" OD, the top of my cutout measure 3-3/4" from the top edge of the fascia and its 7" wide

Next lower the mufflers. To do this, I put a jackstand underneath the exhaust pipe by the rear end. There is a bend there that angles out towards the rear of the car, I thought that was the best place to bend it. You will need a torch set to get this area really hot. Heat it till it is glowing red all around the bend (roughly 270 degrees around the circumference). Be careful though, if you get it too hot in one place you can burn a hole thru it. Once you start to see a puddle, keep moving or you will go past the point of no return. Once it is hot enough, grab the end of the muffler and pull down. You should see a ripple starting to form on the bottom of the bend. Check and see if your mufflers are low enough at this point.

Step 8:

Even up the tips. I had a piece of 6ft long aluminum 2"x2" angle I used to make sure the ends were parallel and that the bottom of the tips were level with each other. Make sure they are centered in the cutouts with equal gaps around them - I used my fingertips to gage clearance. Tack tips into place, remove exhaust system and finish welding tips in.

Step 9:

Figure out how your your going to reuse the mounts to hold the mufflers. For the rubber ones by the rear end, I used 2 5/16" washer for each stud as spacers, and on the rear clamp style hangers I fabbed up a spacer to reuse the original clamp on the seam. Sorry no pic.


Thats all there is to it - seems easy huh

Before I get to the finished pics, here are the lessons learned.
1) Clean the metal before welding. Once I welded my tips on, my welder finally worked the way it should, it was then I realized it was acting up because of the dirty material....
2) Sketch out your tips and then draw your cutout, transfer it to the fascia for a guide. I used Autocad, but it was a day too late

Now for the final pics






SInce I have finished, I noticed the right side is not centered anymore in the cutout when the car is cold. After driving for awhile and once the exhaust is hot - it ends up almost being centered so I have to tweak the mounts a bit to get the best of both worlds.

Driving impressions - its fairly quite. It definately has a different sound to it at idle, very low frequency and somewhat high pressure levels coming out of it. You can't really notice a difference in sound inside the car till about 4k rpm's and then its noticeable, but not loud by anymeans. 5k is still a bit subdued, but almost right. I haven't taken it up to redline yet because of the new trans, but the video clip will let your hear everything (still in the works).

Someday I might get another fascia to cut so it matches my tips, or I might look into an aftermarket one, but for now I am fairly happy with it. I wasn't sure if I was going to like the tips, but my new sig pic looks nice.

Previous posts:
3rd post about exhaust
2nd post about exhaust
1st post about exhaust

2000 740iL - 146k miles & counting, 2 10" JL audio DVC subs and big RockFord Fosgate amp :)
5% tint back 3 windows, 30% on front doors

• Full Muffler Writeup with pics (pic) (url) - rhett 2005-10-15 16:57:20 (10423 views)
  • Awesome. E38.org!! (nt) - 740sporter 2005-10-17 10:54:57 (365 views)
    • That was my goal to have a permanent place on E38 - lol (nt) - rhett 2005-10-17 12:53:44 (342 views)
      • You have my vote my friend. Great job! (nt) - 740sporter 2005-10-17 13:27:45 (290 views)
  • Excellent write up & pictures! No need for tubs of vasilene here! LOL! (nt) - HighLine740iL 2005-10-16 10:22:02 (360 views)
  • Lookin' good Rhett but how do you top all this? Whats next? (nt) - alicat 2005-10-15 20:58:20 (328 views)
    • Heated front seat retrofit more than likely (nt) - rhett 2005-10-16 13:17:29 (282 views)
  • Very nice write up...How's that tranny? (nt) - johngoga 2005-10-15 17:22:36 (326 views)
    • Better than the old one shifts are much better and reverse is 100% (nt) - rhett 2005-10-15 17:38:38 (377 views)
  • Here is 2 pics that I missed (pic) - rhett 2005-10-15 17:01:42 (1059 views)
    • Rhett you need a new sig now. :-) (nt) - kingdom7 2005-10-16 10:10:21 (317 views)
      • your right, I changed the pic - but I need to mention the exhaust mod (nt) - rhett 2005-10-16 22:33:13 (375 views)
    • Re: Here is 2 pics that I missed - Claudio 2005-10-15 17:27:33 (495 views)
      • Did you drop them slightly or remove the exhaust completely? - ChicagoE38 2005-10-16 12:43:39 (328 views)
        • Re: Did you drop them slightly or remove the exhaust completely? - Claudio 2005-10-16 16:01:10 (359 views)
        • Dropped the exhaust completely - see inside for how to change the cats - rhett 2005-10-16 13:16:47 (462 views)
          • There is no need remove entire exhaust system - Claudio 2005-10-16 23:01:06 (546 views)
          • Re: Dropped the exhaust completely - see inside for how to change the cats - Claudio 2005-10-16 16:09:30 (479 views)
      • I will try and post a sound clip on Sunday (tomorrow) - rhett 2005-10-15 17:40:38 (480 views)