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      10-29-2015, 09:20 AM   #1
Asbjorn
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My attempt at creating a slightly louder left muffler

Top down, the 35i with de-catted mid-pipes sounds noticeably better from the passenger seat on the right. It is unfair, and it has to end.

The problem is that the left side muffler is at least twice as big as the right side muffler and has no by-pass system (can flap). This means the right side exhaust is louder than the left, especially when the flap is open. The flap is almost always open at idle, during WOT and in 1st and 2nd. It is not open during cold start or when cruising in 3rd or higher gears.

So one solution is getting an 35is or aftermarket muffler. Here is my attempt at a solution costing a bit less:

Three dollars worth of prototypes...



The perforations inside the muffler that helps to dampen the sound.



You guessed it:



The result



My exhaust has stock down-pipes and mufflers. The mid-pipes have been replaced with Miltek de-catted mid pipes making both sides louder.

This mod has increased the overall exhaust volume slightly. The left muffler however still sounds a little bit louder at idle. The combined system doesn't drone, and is about as inaudible as the stock exhaust when just cruising top up.
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Last edited by Asbjorn; 10-31-2015 at 09:15 AM..
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      10-29-2015, 10:58 AM   #2
golftdibrad
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Your pics are broken.

Please fix! I just got my z4 about a month ago, and its my one complaint about the car, its too quiet. So I'd love to see what your mod is.

I'm keeping stock cats, just want a little more volume.
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      10-29-2015, 11:55 AM   #3
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Quote:
Originally Posted by golftdibrad View Post
Your pics are broken.

Please fix! I just got my z4 about a month ago, and its my one complaint about the car, its too quiet. So I'd love to see what your mod is.

I'm keeping stock cats, just want a little more volume.
Congratulations on your new Z4!

The pics should be fixed now. Let me know if you get a chance to try out this mod. I am pretty sure it won't give you enough volume, but at least it is very easy and inexpensive to try. I highly recommend the secondary cat delete.
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      10-29-2015, 12:22 PM   #4
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stupid double post, sorry...see below

Last edited by golftdibrad; 10-29-2015 at 12:32 PM..
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      10-29-2015, 12:32 PM   #5
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Working now. Thanks. Fantastic idea. Is that a part you bought pre-cut or did you just pick up a bit of tube from an autoparts stare and so some work with the cutoff wheel ?
Might try this before just cutting off the mufflers in favor of straight pipes. Will be way cheaper too....
What size pipe did you use?
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      10-29-2015, 09:41 PM   #6
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Very ingenious, indeed! Some people over on the E9X side have actually been doing this for some time. It's actually similar to the PE Exhaust Mod. By covering the perforation, you are essentially creating a straight pipe (ala muffler delete). However, you still have the added benefit of some muffling since some sound will still be dampened by the dampening material inside.

If you want a louder/more permanent fix, you can also cut the muffler open from the top, then cover the perforations with header wrap and weld everything back on. Or for even more sound, another option is to completely switch the perforated tubing with a solid tube (which is what I initially wanted to do when I bought a 35is)
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      10-30-2015, 05:02 AM   #7
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Quote:
Originally Posted by golftdibrad View Post
Working now. Thanks. Fantastic idea. Is that a part you bought pre-cut or did you just pick up a bit of tube from an autoparts stare and so some work with the cutoff wheel ?
Might try this before just cutting off the mufflers in favor of straight pipes. Will be way cheaper too....
What size pipe did you use?
I believe it was 5.5cm but I forgot to measure the final pipe diameter. I expanded it a bit by hand to make it a tight fit. It was just made with a cutoff wheel at a random shop near my home.
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      10-30-2015, 10:33 AM   #8
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Good stuff.

I looked into the muffler last night and the perforations go past a turn in the pipe, and i dont think covering the one little straight section will help alot. I need to just get the car on stands and look at it. If i can pull off the stock part, cutting the mufflers to remove packing and/or cover the holes with header wrap sounds like a winning plan.
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      10-30-2015, 11:28 AM   #9
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Quote:
Originally Posted by golftdibrad View Post
Good stuff.

I looked into the muffler last night and the perforations go past a turn in the pipe, and i dont think covering the one little straight section will help alot. I need to just get the car on stands and look at it. If i can pull off the stock part, cutting the mufflers to remove packing and/or cover the holes with header wrap sounds like a winning plan.
Ahh yes, I just went down and checked. There is indeed another set of perforations back there. I will see if I can cover those as well by tomorrow.
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      10-31-2015, 01:53 AM   #10
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So I managed to cover the second set of perforations by simply pushing the first tube further in. It almost got stuck where the pipe turns but I managed to get it past. I then added another tube that covers the original area.

The sound volume has increased noticably and is now more or less the same as the right side muffler. I feel very happy with the sound now.

Unfortunately I also hear some metallic rattling at certain rpms. I will try and find out where it is coming from later. Fortunately it is only there occasionally.

EDIT: I found out what caused the rattling. It was the tube that I pushed past the turn to cover the inner perforations. It has now gotten stuck in a new position by itself and no longer rattles. The sound is amazing, especially at high RPMs.

Last edited by Asbjorn; 10-31-2015 at 09:19 AM..
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      11-02-2015, 07:23 AM   #11
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Quote:
Originally Posted by Asbjorn View Post
So I managed to cover the second set of perforations by simply pushing the first tube further in. It almost got stuck where the pipe turns but I managed to get it past. I then added another tube that covers the original area.

The sound volume has increased noticably and is now more or less the same as the right side muffler. I feel very happy with the sound now.

Unfortunately I also hear some metallic rattling at certain rpms. I will try and find out where it is coming from later. Fortunately it is only there occasionally.

EDIT: I found out what caused the rattling. It was the tube that I pushed past the turn to cover the inner perforations. It has now gotten stuck in a new position by itself and no longer rattles. The sound is amazing, especially at high RPMs.
Cool, thanks for reporting back!

I might try this....vs pulling the mufflers and cutting them open.
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