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      12-04-2019, 05:13 PM   #1
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Equal-length exhaust discussion: new S55 sounds

Hi all,

A few members in another thread and I have been in discussion about why the S55 sounds the way it does, no matter what the current aftermarket solutions offer: the same variation of the S55 exhaust note, only variances in volume and rasp control, but the same mono-toned/one-dimensional sounding exhaust note that sounds like two inline 3's.

Inline 6's naturally have evenly spaced exhaust pulse, so in order to take advantage of this and the resulting smooth and more full noise, you simply need to create equality within both banks on a twin turbo set-up to capture this smooth and more full sounding noise. If you deviate from this, you skew the sound more towards having 2 independent inline 3's competing for noise (or current S55 exhaust notes).

There is a bit of a variance between the front and rear bank downpipes, almost a foot and a half, and enough where it creates unequal-length and therefore unevenly spaced pulses when they merge at any form of crossover system: stock, single mid-pipes, double x-pipes, aftermarket X-pipe or rear-section solutions. no matter what is used, sound waves move at the same rate exiting the system so these crossover sections are simply creating a higher-pitched inline 3 sounding exhaust because they never merge in equally spaced pulses, instead they simply allow both banks to crossover in unequally spaced pulses because they don't fix the variance in exhaust lengths between both banks.

It never sounds smooth, it never sounds exciting, and most of all, it never sounds like a 6 cylinder sports car exhaust note like a B58/N55/N54 or to an extent, an RB26/2JZ inline-6 noise. In fact, it basically sounds like a truck-ish V6 exhaust note where they have un-equal length downpipes to create that off-set and the resultant noise.

The solution to this is to create equal-length exhaust pipes before they merge, just like in any other exhaust system on other platforms. A few of us have ventured into this, adding length to the passenger side rear section and creating a new crossover section to create an exhaust note that's never been akin to the "S55 sound" (aside from single-turbo S55's which naturally capture this equally-spaced exhaust pulses).

Equal-length exhaust with stock downpipes, stock midpipes, all catalytic converters intact, stock muffler videos:

(2nd through the middle of 3rd gear, not enough road)


(1st, 2nd, and through the middle of 3rd gear, not enough road)


and a medium throttle fly-by between 5,000-5,500rpm:



Here is an example of exhaust note revs where there is a stock, then a popular single mid-pipe, and then an equal-length exhaust set-up, all of them on stock mufflers and stock downpipes:



And cruising around 5,000rpm with a microphone near the exhaust:





Here is one from another member, the 1st part of the video is unequal-length exhausts pipes, and the 2nd part is equal-length exhaust. You can tell the difference in pitch and tone where the equal-length exhaust there is a higher pitch noise , like it enjoys being revved like a sports car should, this one has catless downpipes and it really shows more of how much the exhaust note changes





There are others who have ventured into this where they utilized an aftermarket muffler to where our S55's start to sound like RB26/2JZ-like in tone. Anyways, let's discuss set-ups.

This is essentially what was done on my set-up, drawing is terrible I know, but the red represents the new pipes to create the near equal-length piping before it merges at a crossover:



The U-bend that changed the sound altogether (prototype version 1 photo), you'll want a near 14" compensation on the LHD passenger side for to be close to equal to the drivers side when all said and done.



More PROTOTYPE photos of the bend and merge:

CLICK ME

and another

CLICK ME


I'll continually update this post once more development occurs or if I have new videos that capture the sound better.

This thread was to get the discussion continuing since the "starters" including myself had to take a custom approach as no after solutions are currently available. Post your equal-length/near equal-length set-ups, and let's keep it to that topic only.
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      12-04-2019, 05:19 PM   #2
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Picture of the recording device on these videos



Better and longer video clips would probably help. The equal length videos reminded me more of E46 M3 exhausts honestly and what they sounded like which could be a good thing for a lot of people but would need to hear better quality audio for sure.
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      12-04-2019, 07:21 PM   #3
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Here’s my contribution.

Current (V2) Specs:
- Stock primary cats
- OEM midpipe cut after secondary cats location
- Secondary cats are replaced with Magnaflow 14156 resonators
- Measured from downpipe connection, the US passenger side pipe is 14 inches longer than driver's side pipe before merging into 1 single 3.0 inch pipe
- Custom muffler from TopGear Motorworks. 3.0 inch inlet & outlet
- Outlet is 3.0 in -> 2 x 4.0 in dual walled rolled tips






V1 (previous version) - Sounds 2JZ down low, and S54 up high:






Exhaust design attached in photo. V2 shown. V1 is similar but with larger muffler with 4.0 inch exit and and 4.0 inch single walled tip.
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Last edited by ntg44; 12-30-2019 at 11:33 AM..
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      12-04-2019, 09:16 PM   #4
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Quote:
Originally Posted by spool twice View Post
Hi all,

A few members in another thread and I have been in discussion about why the S55 sounds the way it does, no matter what the current aftermarket solutions offer: the same variation of the S55 exhaust note, only variances in volume and rasp control, but the same mono-toned/one-dimensional sounding exhaust note that sounds like two inline 3's.

Inline 6's naturally have evenly spaced exhaust pulse, so in order to take advantage of this and the resulting smooth and fuller noise, you simply need to create equality within both banks on a twin turbo set-up to capture this smooth and fuller sounding noise. If you deviate from this, you skew the sound more towards having 2 independent inline 3's competing for noise (or current S55 exhaust notes).

The reason behind this is that there is a bit of a variance between the front and rear bank downpipes, almost a foot and a half inch, and enough where the unequal-lengths create unevenly spaced pulses when they merge at any form of crossover system (stock, single mid-pipes, double x-pipes, aftermarket X-pipe or rear-section solutions), no matter what, sound waves move at the same rate exiting the system so these crossover sections are simply creating a higher-pitched inline 3 sounding exhaust because they never merge equally spaced exhaust pulses, instead they simply allow both banks to crossover in unequally spaced pulses because they don't fix the variance in exhaust lengths between both banks.

It never sounds smooth, it never sounds exciting, and most of all, it never sounds like a 6 cylinder sports car exhaust note like a B58/N55/N54 or to an extent, an RB26/2JZ inline-6 noise. In fact, it basically sounds like a truck-ish V6 exhaust note where they have un-equal length downpipes to create that off-set and the resultant noise.

The solution to this is to create equal-length exhaust pipes before they merge, just like in any other exhaust system on other platforms. A few of us have ventured into this, adding length to the passenger side rear section and creating a new crossover section to create an exhaust note that's never been akin to the "S55 sound" (aside from single-turbo S55's which naturally capture this equally-spaced exhaust pulses).

Here is an example of exhaust note revs where there is a stock, then a popular single mid-pipe, and then an equal-length exhaust set-up, all of them on stock mufflers and stock downpipes:



Another one in 2nd and 3rd gears:



And cruising around 5,000rpm with a microphone near the exhaust:





Here is one from another member, the 1st part of the video is unequal-length exhausts pipes, and the 2nd part is equal-length exhaust. You can tell the difference in pitch and tone where the equal-length exhaust there is a higher pitch noise, like it enjoys being revved like a sports car should





There are others who have ventured into this where they utilized an aftermarket muffler to where our S55's start to sound like RB26/2JZ-like in tone. Anyways, let's discuss set-ups.

This is essentially what was done on my set-up, drawing is terrible I know, but the red represents the new pipes to create the near equal-length piping before it merges at a crossover:

[img]https://f80.bimmerpost.com/forums/pi...ictureid=72215[/img]

The U-bend that changed the sound altogether:

[img]https://f80.bimmerpost.com/forums/pi...ictureid=72216[/img]


I'll continually update this post once more development occurs or if I have new videos that capture the sound better.

This thread was to get the discussion continuing since the "starters" including myself had to take a custom approach as no after solutions are currently available. Post your equal-length set-ups, and let's keep it to that topic only.
I don't know much about acoustical engineering but everything you're saying is making an incredible amount of sense. God I hope someone is out there working on the best equal length exhaust system with an mpe setup. I love how throaty my MPE is. I can't imagine it being better, but this post makes me think there's room for improvement!
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      12-05-2019, 06:11 AM   #5
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Quote:
Originally Posted by moonshine89 View Post
I don't know much about acoustical engineering but everything you're saying is making an incredible amount of sense. God I hope someone is out there resting the best equal length exhaust system with an mpe setup. I love how throaty my MPE. I can't imagine it being better, but this post makes me think there's room for improvement!
In theory, a midpipe could be made to mate to the MPE, but that seems like a limited market compared to something like the AA midpipe which mates to most axle back systems. I think that would involve cutting up the MPE to mate to it, but I'm sure some people would be more comfortable with this than others for the sound benefit.

The other issue I see is that the stock muffler and MPE were designed for the stock tone - changing to equal length changes this considerably, and I'm not entirely sure that a chambered design that is made for stock lengths is going to work for equalized lengths. Just listen to the difference between mine and spool twice's systems - they sound almost nothing alike. My system has a long single pipe to blend the tones, and that's different than the X pipe in spool twice's design. Add a different muffler, and we're not even similar anymore.

I've been trying to procure an AA Signature rear muffler with the single entrance - I think this is the most successful I'm going to get to a valved dual exit system at my budget. Problem is I really don't want to buy new, since the muffler will most likely cost more than my entire custom system, and I don't care *that* much about valves and dual exits - tone trumps everything to me, and it's a work in progress to get one good tone, let alone iterating until both open and closed valve tones are acceptable. Maybe if I was a die hard M enthusiast who planned on keeping the car forever, but I'm not.
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      12-05-2019, 06:11 AM   #6
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Quote:
Originally Posted by ntg44 View Post
Here’s my contribution: equalized lengths merged into a single pipe, single exit exhaust. Sounds 2JZ down low, and S54 up high:
Had a chance to compare exhaust notes on my last weekend cruise with an M2 competition (stock exhaust), and 2 S54 E46 M3's both with headers + exhaust.

In person, my exhaust sounds almost like a combination of an N54 + headered-S54 downlow, midrange, and uptop, only more muffled and with a lower octave overtone (S55 OE muffler challenge). S54's sort of sound like a grumbly 6 cylinder down low with euro-headers (or any headers for that matter), but they both sound really smooth and good in the mid-high range, except they can rev to 8,000rpm

I wish the equal-length pipes paired with the OE muffler would produce more of a 2JZ noise down low like your set-up, but the design/internals of the muffler wasn't made to accentuate that noise given how it was designed around cancelling out the inherit rasp that the OE unequal-length design naturally induces (basically its designed to muffle out higher notes).
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Last edited by spool twice; 12-05-2019 at 06:22 AM..
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      12-05-2019, 06:17 AM   #7
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Quote:
Originally Posted by spool twice View Post
I wish the equal-length pipes paired with the OE muffler would produce more of a 2JZ noise down low like your set-up, but the design/internals of the muffler wasn't made to accentuate that noise given how it was designed around cancelling out the inherit rasp that the OE unequal-length design naturally induces (basically its designed to muffle out higher notes).
I'm curious to get my car back today with the smaller muffler. We changed some piping diameters, tip style, and muffler size to hopefully reduce the bassier frequencies and bring out the higher ones. Also hopefully this resolves my 3500rpm rasp issue - really hope it was the single walled 4 inch tip that was the problem.

Hopefully this brings out more 2JZ/RB at high revs, but I won't complain if it's just a louder version of what it is now - a twin turbo M3 sounding naturally aspirated is an achievement in itself haha.
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      12-05-2019, 06:18 AM   #8
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Quote:
Originally Posted by ntg44 View Post
The other issue I see is that the stock muffler and MPE were designed for the stock tone - changing to equal length changes this considerably, and I'm not entirely sure that a chambered design that is made for stock lengths is going to work for equalized lengths. Just listen to the difference between mine and spool twice's systems - they sound almost nothing alike. My system has a long single pipe to blend the tones, and that's different than the X pipe in spool twice's design. Add a different muffler, and we're not even similar anymore.
I can attest that even with a single merge pipe design, the OE exhaust will still have a blend of smooth equal-lengthed sound qualities alongside a lower-S55 undertone. Definitely the OE muffler wasn't designed for the change in character that equalizing the pipe length induces, definitely an improvement over stock or current aftermarket mid-pipe designs as my rev video above shows, however definitely not along the lines of starting fresh with a non-chambered muffler.

I can attest this because my curiosity got me to block off one side of my exhaust tips, forcing the exhaust to exit one side (essentially creating a single-pipe design after they merge). I can make a video of it if anyone wants to hear it.

Cliff notes: OE or MPE mufflers will likely not produce 100% that 2jz noise, however it does sound something in-between an N54/S54 combination.
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      12-05-2019, 06:54 AM   #9
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Quote:
Originally Posted by spool twice View Post
I can attest this because my curiosity got me to block off one side of my exhaust tips, forcing the exhaust to exit one side (essentially creating a single-pipe design after they merge). I can make a video of it if anyone wants to hear it.

Hey spool twice, you just gave me an idea for your system.

Everyone wants dual exits and valves, so if you're willing to hack up your stock muffler (easily reversible to weld back together) - check out my mockup of your setup.

Red: Cut exhaust here
Yellow: New routing and muffler


All it looks like it needs is a 2 entrance, 2 exit muffler, 2 Y exhaust tip pipes, and like 8 inches of piping? Seems simple enough for any welder to accomplish. What if this is all you need?

Let me know your thoughts.
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      12-05-2019, 07:42 AM   #10
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Quote:
Originally Posted by spool twice View Post
I wouldn't know where to find a muffler with a inlet & outlets of that nature in the aftermarket world, looks great though
I'm picking up my car today - do you want me to ask my fabricator for you? He can use my stock exhaust as a reference point to measure out the pipe distances for inlet/outlet and make one for you. Then, I'll just get him in contact with you for billing and I can ship it for you. He can probably even do the tips with muffler connection as well - all your fabricator would need to do is connect the 4 pipes to the muffler.

PM me if you're interested. Happy to help. This probably wouldn't cost as much as you think. M tax really shifts people's perspective on what affordable is.
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      12-05-2019, 08:45 AM   #11
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Equalize exhaust lengths definitely makes the S55 motor sound better. Personally I like the exhaust characteristic of the S55.
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      12-05-2019, 11:48 AM   #12
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Could potentially find two smaller mufflers with a single inlet and offset exit. I haven't searched too much because its kind of abstract, but they're out there.
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      12-05-2019, 11:56 AM   #13
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Quote:
Originally Posted by sicck_f82 View Post
Equalize exhaust lengths definitely makes the S55 motor sound better. Personally I like the exhaust characteristic of the S55.
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      12-05-2019, 12:03 PM   #14
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Quote:
Originally Posted by Kilabyte View Post
Haha, I realize your post is a little tongue in cheek, but I just came across David Patterson's newest video of the R32 Skyline GT-R (ThatDudeInBlue). Take a listen to the TT R32:



It really doesn't sound that different from the S55. I realize different configurations give it that awesome harmonic F&F sound, but the S55 is closer to the car in that video than most people would probably admit. The S55 just has some strange resonance in some areas that are amplified at the wrong time - otherwise the tone is pretty darn similar.
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      12-05-2019, 02:26 PM   #15
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Quote:
Originally Posted by ntg44 View Post
I'm picking up my car today - do you want me to ask my fabricator for you? He can use my stock exhaust as a reference point to measure out the pipe distances for inlet/outlet and make one for you. Then, I'll just get him in contact with you for billing and I can ship it for you. He can probably even do the tips with muffler connection as well - all your fabricator would need to do is connect the 4 pipes to the muffler.

PM me if you're interested. Happy to help. This probably wouldn't cost as much as you think. M tax really shifts people's perspective on what affordable is.
Down the line perhaps, right now I'm just enjoying the modded "stock" sound and will likely milk it for what it's worth considering it was only $460-$470 on my end and doesn't sound like the next S55 I meet in traffic or at meets

I am trying to get a better recording device though, cellphones + inexpensive external mics aren't the best. I'm sure you know what your set-up, there is so much more depth to the sound that's not being captured appropriately on video, particularly the higher notes being harder to capture.
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      12-05-2019, 02:28 PM   #16
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The awesome thing about the RB26 is that they too come stock with unequal-length downpipes. If you youtube their exhaust sounds, you can see how the stock RB26 sounds similar to an S55 (minus the rasp), whereas the equal-length downpipes change the sound altogether.

Now, if only we had options for equal-length downpipes...that would eliminate potential variances in equal-length designs as I'm sure I've deviated from 100% with my design with me only adding 14" of total passenger side effective length

also, looping back to this video from another member who has catless downpipes but OE muffler, I think the OE muffler can overcome the low-octave overlay as it may be produced by the having cats intacted themselves. Now I wonder how his exhaust sounds fully catless and with appropriate resonators (he still has secondary cats), the before/after on his is pretty dramatic in my opinion with regards to the change in pitch and overall tone:

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      12-05-2019, 07:17 PM   #17
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Update: Just got my car back from my fabricator. V2 design in attached photo.

Changes from V1 include:
- smaller muffler
- changed exit side pipe from 4.0 in -> 3.0 in, matching the entrance side pipe
- Changed exhaust tip style from 1 single walled 4.0 inch tip to 2 x 4.0 inch double walled rolled tip


Goals of V2 Design:
- Reduce bassier frequencies and boominess
- Eliminate 3500 RPM rasp/resonance
- Make exhaust louder


Results of V2 Design:
- Exhaust is louder, in such an awesome way. No increased drone from V1, but a reduction of bassier frequencies and replaced with higher pitched tones. In my opinion, it sounds just like an RB26 from the inside and out, up to about 4000 RPM. After that, the tone goes nuts. I'm not super familiar with the N54/55 tones, but to me it sounds like a 2JZ if it was a little muddier/dirtier. But it doesn't sound as mechanical as the V1 tone, at least from my initial observations.

- 3500 RPM rasp/resonance is still there. But somehow it isn't louder than before at least from the inside, and since the exhaust as a whole is louder, it gets drowned out a little better. Not perfect, but eh, I'll take it.


The car is louder now, but that just makes driving with windows down on the 30 minute drive home in 45 degree Chicago weather all the more worth it. Even accelerating lightly from a stop puts a huge grin on my face.


Luckily, my fabricator had a GoPro in the shop, so we stuck it on the bumper and drove around for a bit. I'm waiting for the video, but we listened to it on the shop speakers after pulling back in, and from what I heard today - it's good. It's very, very good. He's supposed to send me the video sometime soon - I'll get it up on YouTube as soon as I can - you all need to hear this. I couldn't be more excited to share this with all of you who are following.
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      12-05-2019, 07:32 PM   #18
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Quote:
Originally Posted by ntg44 View Post
Update: Just got my car back from my fabricator. V2 design in attached photo.

Changes from V1 include:
- smaller muffler
- changed exit side pipe from 4.0 in -> 3.0 in, matching the entrance side pipe
- Changed exhaust tip style from 1 single walled 4.0 inch tip to 2 x 4.0 inch double walled rolled tip


Goals of V2 Design:
- Reduce bassier frequencies and boominess
- Eliminate 3500 RPM rasp/resonance
- Make exhaust louder


Results of V2 Design:
- Exhaust is louder, in such an awesome way. No increased drone from V1, but a reduction of bassier frequencies and replaced with higher pitched tones. In my opinion, it sounds just like an RB26 from the inside and out, up to about 4000 RPM. After that, the tone goes nuts. I'm not super familiar with the N54/55 tones, but to me it sounds like a 2JZ if it was a little muddier/dirtier. But it doesn't sound as mechanical as the V1 tone, at least from my initial observations.

- 3500 RPM rasp/resonance is still there. But somehow it isn't louder than before at least from the inside, and since the exhaust as a whole is louder, it gets drowned out a little better. Not perfect, but eh, I'll take it.


The car is louder now, but that just makes driving with windows down on the 30 minute drive home in 45 degree Chicago weather all the more worth it. Even accelerating lightly from a stop puts a huge grin on my face.


Luckily, my fabricator had a GoPro in the shop, so we stuck it on the bumper and drove around for a bit. I'm waiting for the video, but we listened to it on the shop speakers after pulling back in, and from what I heard today - it's good. It's very, very good. He's supposed to send me the video sometime soon - I'll get it up on YouTube as soon as I can - you all need to hear this. I couldn't be more excited to share this with all of you who are following.
Lemme heart it. I'm excited for this.
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      12-05-2019, 08:09 PM   #19
ntg44
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Well, that was sooner than expected.

VIDEO IS UP! Make sure to listen on YouTube and check the comment section for time stamps. It gets right to the juicy parts.

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      12-05-2019, 08:21 PM   #20
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Wow that sounds really really good. I'd never recognize that as an F80 if someone played it for me. Very nice! You might become rich if you can get this made and sold.
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      12-05-2019, 08:24 PM   #21
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Quote:
Originally Posted by Zoli007 View Post
Wow that sounds really really good. I'd never recognize that as an F80 if someone played it for me. Very nice! You might become rich if you can get this made and sold.
Already in talks with Top Gear Motorworks about it. We'll see how this turns out, but they definitely have earned it. Completely craps on every single friggin exhaust out there.
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      12-05-2019, 09:06 PM   #22
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Quote:
Originally Posted by ntg44 View Post
Quote:
Originally Posted by Zoli007 View Post
Wow that sounds really really good. I'd never recognize that as an F80 if someone played it for me. Very nice! You might become rich if you can get this made and sold.
Already in talks with Top Gear Motorworks about it. We'll see how this turns out, but they definitely have earned it. Completely craps on every single friggin exhaust out there.
Wow that sounds awesome I'd love this but my ocd needs the 2 sets of valved exhaust tips so the my wife and kids will still go out in my car
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msdss168.00

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