building my own exhaust 128i

[neverdone]

I'm a welder by trade but I've never made an exhaust and the 1er will be my first project. I'm just going to do a cat back just to get a bit of noise. My question is, what size pipe should I use and what muffler should I look at for a DIY?

I haven't even looked under the car yet to see what I'm getting into, it might just be mostly bending and clamps for all I know. Anything else I should know before I go ahead with this?

[SayHack]

I once had a 95 M3, and took it to an exhaust shop (keep in mind I was 18 back then) and the guy suggested he make me a custom catback, with a single 2.75 inch pipe, attached to an adopter to connect to factory cats. And the tip was "DTM" stile, with dual titanium tips. I know it sounds horrible, but a lot of people (including people with e36 M3 that were in their mid to late 30s) asking me what exhaust I had on that because it sounded so "bad a$$). My dad used to tell me that he can hear me downshifting from a block away. I am not sure how loud you want it to be, but N51/N52 engines are very similar to the s50 in the e36 M3. Just throwing it out there.

[Taskmaster]

Single 3" With muffler and resonator in line.

[neverdone]

What muffler should I use?

[Tchao]

All modern (24v) BMW inline 6's needs resonator(s) if you want it to sound good.
If you're staying naturally aspirated, 2.50" is plenty plenty big.

Keep emissions in mind if you're doing a full exhaust.
Even if you aren't restrained by emissions, you want a high flow cat (100-200cell) if you don't want your car to smell like an old lawn mover.

After some headers...
I plan to to keep my OEM secondaries then Y pipe them to a single 2.50" with

Option A:
Two inline magnaflow universal muffs as resonators.

Option B:
A single dynomax turbo muffler as resonator.

Then a Vibrant stainless as the final muffler.

Just tossing some ideas around.

[631twentyeighteye]

If i ever get around to do the full exhaust(headers back), i want to try a big ol resonator like a cherrybomb to take out most of the rasp. And then just straight pipe to the tips. If that's too loud i'll add in a muffler before the exhaust tips.

[mike@x-ph.com]

Good luck and let us know how it goes

[andrey_gta]

There was a thread here that referenced a Nissan 350z NA build exhaust.
The best result used stepped headers into a stepped exhaust was described as the following ms paint attempt:

The Muffler section was a 5 inch long trumpet section that was a curve, unlike the linear diagram. The article argued that the curved design had some gain over a linear, but for production a linear is easier.

Also there is a formula to capture drone and calculate placement of a resonator to capture the sound wave

[Taskmaster]

Originally Posted by andrey_gta

There was a thread here that referenced a Nissan 350z NA build exhaust.
The best result used stepped headers into a stepped exhaust was described as the following ms paint attempt:
Attachment 1167580
The Muffler section was a 5 inch long trumpet section that was a curve, unlike the linear diagram. The article argued that the curved design had some gain over a linear, but for production a linear is easier.

Also there is a formula to capture drone and calculate placement of a resonator to capture the sound wave

I posted that:

http://www.e90post.com/forums/showthread.php?t=964717
The trumpet changes the way the exhaust diffuses energy causing a slight power gain.


And if it where me, a Magnaflow or Borla muffler. If you aren't keeping the stock headers, consider adding in a inline high flow cat. Go with 3" piping for maximum gains (even though the piping after the Y pipe doesn't matter in terms of peak) too small a pipe can reduce peak.

[andrey_gta]

Originally Posted by TheAxiom

I posted that:

http://www.e90post.com/forums/showthread.php?t=964717
The trumpet changes the way the exhaust diffuses energy causing a slight power gain.

Excellent, Thanks for linking