Equal-length exhaust discussion: new S55 sounds

[ntg44]

Originally Posted by MyFragileHalogen

A noob question: although my exhaust sounds low pitched, from driver seat, I can hear engine noise (which also ASD will amplify) that is at higher overtone. Is what this EQ exhaust design doing bringing out more of the higher tone? On the web I could find some videos of ridiculous sounding Skyline GT-R with exhaust pipes just directly coming out through hood. Or, like ridiculously howling rally cars, if we do the same thing to F8x, do we get that sort of very high-pitched howling tone? (at excessively non-livable loudness)

I'm not sure how to answer your question. Listen to a YouTube video of stock exhausts then compare them to our equal length videos on the first page of this thread. The difference is obvious, all though I'm not sure how that relates to your question.

[ntg44]

Originally Posted by Kev608

I just played these videos in full 7.2.4 Dolby Atmos and I am slightly errect. Great work!

Thank you Soon it will be available to the masses. We are so close.

[MyFragileHalogen]

Originally Posted by ntg44

I'm not sure how to answer your question. Listen to a YouTube video of stock exhausts then compare them to our equal length videos on the first page of this thread. The difference is obvious, all though I'm not sure how that relates to your question.

Your car does sound very nice and I have no doubt on your achievement. I am just finding it fun at reading about exhaust note tuning stuff online and thinking of anything that can be related to improving sound of our cars. My knowledge about engines and exhausts is very little so it's fun to learn.

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Here's some of interesting (or silly) stuff I found. These are not validated so you guys please correct me.

1) "normal exhausts have mufflers which silence all sounds while most aftermarket exhausts will silence all high tones to give that deep bass sound. So get widest piping and add an extra pipe to silence the bass sound"
(source) https://www.bosozokustyle.com/2009/1...kusha-muffler/

2) Some shop guy answering about few things:
1. what effect does exhaust material have on the sound?
2. X or H pipe
3. Header length and diameter
4. tail pipe volume diminishing the closer you get to the tail pipe to help keep the gas velocity up to help with scavenging and maintain torque
5. how much does a turbo affect the sound level, sound quality & sound tone?
6. How about Anti-Reversion?
...
"Cam plays a big role. Exhaust ramp speed, valve overlap, duration, LSA.,...,Exhaust port shape is a big one. Manifold design (equal length, tuned, log) plays a lot. One of the biggest things, though is firing order."
(source) https://grassrootsmotorsports.com/fo.../151667/page1/

3) Firing order of Skyline/Supra vs S55
"The Skyline (RB20/25/26 i.e. the straight 6) and the Supra fire 1 5 3 6 2 4
The S55 in the BMW M4 fired 1 3 5 6 2 4.

So a twin turbo like these would normally fire
1 - bank 1
5 - bank 2
3 - bank 1
6 - bank 2
2 - bank 1
4 - bank 2
That gives perfect alternating firing pulses to each turbine in turn and also pulses from each tailpipe where dual exhausts are used like N54 etc.
However, 135624 is
1 - bank 1
3 - bank 1
5 - bank 2
6 - bank 2
2 - bank 1
4 - bank 2

Very different indeed...... two pulses in turn to bank 1 then two to bank 2, then 1 pulse each then back to the twin pulses......"
(source) https://www.pistonheads.com/gassing/...t=1776603&i=20

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One guy does mention about equal length downpipes for his skyline. If above S55 firing order is true, that does somewhat make sense to uneducated me why it's hard to get exhaust tuning right on S55.

[LRGM3]

Firing order definitely has an effect on exhaust sound. I’ve heard this scenario first hand with a cam swap/firing order change on engines with no other changes being made.

[spool twice]

Originally Posted by Savag303

What is the difference between these two? one sounds a lot deeper than the other. Is this the same set up? Is this set up have the rear h pipe right after the diff or does this have the flowmaster x pipe?

1st video with the stationary rev is an EQ + X-pipe

2nd video is an EQ + H-pipe

Personally, I like the sound of the X-pipe during part throttle situations, but prefer the H-pipe at wide open. The single merge system such as ntg44's seems to be the best compromise between having both though.

[ntg44]

Originally Posted by MyFragileHalogen

One guy does mention about equal length downpipes for his skyline. If above S55 firing order is true, that does somewhat make sense to uneducated me why it's hard to get exhaust tuning right on S55.

I believe your source is misinformed. The firing order for basically all I-6s is 1-5-3-6-2-4. This is the firing order for all modern BMW I-6s. I have not found one technical document to reference the firing order of the S55 engine, but by just looking at the crank shaft, the positions are all the same between N55 and S55. The only other possible firing orders given the crank shaft design would be 1-2-3-6-5-4, 1-2-4-6-5-3, or 1-5-4-6-2-3 which would be a balancing nightmare, and no manufacturer would do this.

There are many reasons for the differences in sound, but firing order is not one of them. Equal length exhausts are getting us much closer though, and it's probably going to be the closest we ever get unless you go single turbo or equal length exhaust manifolds, both of which are pretty impractical in the modern era of turbo hot sides integrated into the manifold and plug and play fitment turbo kits.

[MUTIGER]

Wouldn't this design by active autoworks serve the same function as adding 14" of length to the passenger side exhaust? It would even out the exhaust pulses before the muffler correct? Just curious on peoples thoughts and physics behind this design. Thanks

[ntg44]

Originally Posted by MUTIGER

Wouldn't this design by active autoworks serve the same function as adding 14" of length to the passenger side exhaust? It would even out the exhaust pulses before the muffler correct? Just curious on peoples thoughts and physics behind this design. Thanks

Have you listened to any AA midpipe videos? It's basically a smoother version of the stock exhaust tone. Better, but not the tone that's achieved from equalizing lengths. Since my design is closest in philosophy to AA mid, just compare my videos (3rd post in this thread) to any AA midpipe video and the difference should be apparent.

[MUTIGER]

Originally Posted by ntg44

Have you listened to any AA midpipe videos? It's basically a smoother version of the stock exhaust tone. Better, but not the tone that's achieved from equalizing lengths. Since my design is closest in philosophy to AA mid, just compare my videos (3rd post in this thread) to any AA midpipe video and the difference should be apparent.

I have, I agree, and I appreciate the time and effort put into this. Many thanks to you and Spoolio for changing the conversation about the horrible exhaust noises coming from our $70K+ cars I am still curious and don't understand why the single pipe doesn't solve the issue. The exhaust pulses are combined into a single pipe and then distributed equally to the muffler. I might lose sleep over this...

[ntg44]

Originally Posted by MUTIGER

I have, I agree, and I appreciate the time and effort put into this. Many thanks to you and Spoolio for changing the conversation about the horrible exhaust noises coming from our $70K+ cars I am still curious and don't understand why the single pipe doesn't solve the issue. The exhaust pulses are combined into a single pipe and then distributed equally to the muffler. I might lose sleep over this...

The exhaust gases are, but the sound waves aren't. It's the same reason a flat plane crank Ferrari V8 sounds nothing like an American cross plane V8. It's not the firing order alone that causes Ferrari V8s' exhaust to sound different, it's the way the sound waves blend together as a result of the firing order when everything comes together at the end. All the gases are merged the same way eventually, but the sound waves are completely different.

Here's a video of a Z06 with header trickery to make it sound more like a Ferrari. It's all the same concept, timing the sound pulses differently to achieve a different tone.

[spool twice]

a single mid-pipe such as the AA merges in unequally-spaced exhaust pulses, so it never creates the effect of an equal lengthed design. How the exhaust gases are spaced correctly impacts sound greatly.

The rev comparison video on the 1st post shows the big difference in sound between both.

[MUTIGER]

You guys are awesome...thanks for the explanations

[jrp73]

Originally Posted by MUTIGER

Wouldn't this design by active autoworks serve the same function as adding 14" of length to the passenger side exhaust? It would even out the exhaust pulses before the muffler correct? Just curious on peoples thoughts and physics behind this design. Thanks

Something like this would be a great solution. The sound waves are merged straight after the downpipes it's just where it splits after the single pipe which would need to be "equal-lengthed"

I'd be interested to know the actual lengths of those to see how far out it is

[doughboy]

Originally Posted by jamespheely

Something like this would be a great solution. The sound waves are merged straight after the downpipes it's just where it splits after the single pipe which would need to be "equal-lengthed"

I'd be interested to know the actual lengths of those to see how far out it is

No sir, respectfully, that's not how it works.

That design merges out-of-sync pulses just like the standard system. They need to be kept separate, then one pipe extended, then merged when they are correctly in sync.

The key is to delay pulses from cylinders 4, 5 and 6 only, before merging, but as soon as you merge the pulses that's it - game over, you can't make any timing changes after that because you can't separate pulses from each bank once they have been merged.

[jrp73]

Originally Posted by doughboy

No sir, respectfully, that's not how it works.

That design merges out-of-sync pulses just like the standard system. They need to be kept separate, then one pipe extended, then merged when they are correctly in sync.

The key is to delay pulses from cylinders 4, 5 and 6 only, before merging, but as soon as you merge the pulses that's it, you can't make any timing changes after that because you can't separate pulses from each bank once they have been merged.

Makes sense, I was under the impression it was the due to the length difference after the downpipes which kept the banks out of sync.

So at the point the Downpipe ends it's already unequal length at that point?

[ntg44]

Originally Posted by jamespheely

Makes sense, I was under the impression it was the due to the length difference after the downpipes which kept the banks out of sync.

So at the point the Downpipe ends it's already unequal length at that point?

Correct, which is why it's so friggin hard to package the rest of the exhaust to equalize the lengths later on.

[ntg44]

Update: Well it's official. My M3 is out of my hands for a couple weeks

It's finally happening. Glorious, fully featured equal length cat back exhaust for the masses, all thanks to Top Gear Motorworks and this community. Time to blow up the exhaust market

I'll post updates with progress as I receive them, but until then, you can follow @ topgearmotorworks on Instagram for anything related to this project.

[doughboy]

Awesome. Will it be a quad tip version with integrated valves?

[ntg44]

Originally Posted by doughboy

Awesome. Will it be a quad tip version with integrated valves?

Yep. Everything you'd expect from a mainstream exhaust system, without the garbage tone.

[Schultz28]

Originally Posted by ntg44

The exhaust gases are, but the sound waves aren't. It's the same reason a flat plane crank Ferrari V8 sounds nothing like an American cross plane V8. It's not the firing order alone that causes Ferrari V8s' exhaust to sound different, it's the way the sound waves blend together as a result of the firing order when everything comes together at the end. All the gases are merged the same way eventually, but the sound waves are completely different.

Here's a video of a Z06 with header trickery to make it sound more like a Ferrari. It's all the same concept, timing the sound pulses differently to achieve a different tone.

This. Here is a better example, though.

3:55 to see exhaust/little explanation.
18:15 for exhaust sounds

[doughboy]

Hoonigan, that's a great video, LOL.

From 18mins on...

[TT-Tom]

Originally Posted by ntg44

Update: Well it's official. My M3 is out of my hands for a couple weeks

It's finally happening. Glorious, fully featured equal length cat back exhaust for the masses, all thanks to Top Gear Motorworks and this community. Time to blow up the exhaust market

I'll post updates with progress as I receive them, but until then, you can follow @ topgearmotorworks on Instagram for anything related to this project.

This is great news, I'm buying one asap! Do they have a website or how will we be able to buy this?