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      12-11-2019, 05:42 AM   #89
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Quote:
Originally Posted by spool twice View Post
Just as a forewarning, you will likely get a "wtf" look or a confused facial gesture when you ask an exhaust shop to accomplish this. I had to go to a few, and the one that finally did it was still hesitant and kept saying "In all my 15 years of building an exhaust, adding just an x-pipe will do the same thing".... it won't do the same thing. Just keep insisting on it and just say "if it doesn't accomplish what I want, I can always return it back to stock."

It's an outside-the-box approach to resolve the space constraints.
I can second this. Even TopGear was unconvinced initially, stating that something like the AA midpipe would be the largest change. In the end though, they were interested in trying something new, and it was my money on the line, so they were happy to do what I asked with the caveat that it's not their fault if it doesn't turn out the way I wanted

The easiest way to convince a shop is to show them my video and compare it to any AA midpipe video. Then it'll click.
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      12-11-2019, 11:52 PM   #90
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Quote:
Originally Posted by ntg44 View Post
This is *slightly* off topic, but if you want to hear what a 100% stock exhaust sounds with 2nd cats replaced with the Magnaflow 14156 resonators, here is my previous exhaust video with the valves unplugged and stuck open:





There is a dedicated thread to this (Started by Alan I), so I don't want to de-rail this thread. But for roughly $300 USD installed, you cannot beat this mod as a low budget option. It got rid of all the nasty mid-high range rasp when on boost. It's not exactly what I'd call inspiring, but at least it's fixed. It also got rid of some of the low RPM side effects of open valves - for example, my manual shifter no longer rattles after this modification. Overall, it just makes the exhaust more pleasant and un-farty.
Just to clarify, these are the resonators you are using on your V2 system, correct?
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      12-12-2019, 05:27 AM   #91
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Quote:
Originally Posted by ntg44 View Post
I can second this. Even TopGear was unconvinced initially, stating that something like the AA midpipe would be the largest change. In the end though, they were interested in trying something new, and it was my money on the line, so they were happy to do what I asked with the caveat that it's not their fault if it doesn't turn out the way I wanted

The easiest way to convince a shop is to show them my video and compare it to any AA midpipe video. Then it'll click.
This is why the so called "experts" haven't looked into this.

Because it's just a bit out of their comfort zones. They're not thinking like engineers they're just doing what they always do.
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      12-12-2019, 05:54 AM   #92
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Originally Posted by doughboy View Post
This is why the so called "experts" haven't looked into this.

Because it's just a bit out of their comfort zones. They're not thinking like engineers they're just doing what they always do.
To be fair though, this sort of thing is extremely unconventional. From a performance perspective, nobody would want this. You want as free flowing, straight through pipes as possible with the least amount of bends, in which case the stock exhaust is probably just fine. Sound usually takes a back seat. If I was designing an aftermarket system from nothing, this would probably be the last thing I'd be worried about, given the complexity and packaging challenges and unknown demand at the time for such a product.

Yeah, there's a sound benefit, but that's really the only benefit. If I was an exhaust manufacturer, I'd probably overlook this too. From my experience at least, an actual business owner's perspective is vastly different than a consumer's perspective of a business owner's perspective. Until I own my own exhaust business (not happening), I can't really blame anybody.

At least we can look forward to the near future
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      12-12-2019, 05:57 AM   #93
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Quote:
Originally Posted by 92coupe View Post
Just to clarify, these are the resonators you are using on your V2 system, correct?
Correct. I've recently updated my first post in this thread to include every single relevant detail about my equal length system:

https://f80.bimmerpost.com/forums/sh...97&postcount=3
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      12-12-2019, 08:07 AM   #94
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I'm going to pull the trigger and have mine removed and use those resonators in place, there is room for tonal improvements with mine since I still have all four cats intact currently, its about as good as it will get being legally compliant + having equal-length rear seciton + having an OE muffler. Listening to my exhaust and another members equal-length + OE muffler system and he has catless downpipes, his simply screams and howls up top even with this H-pipe design vs my chambered x-pipe.

ntg44, have you noticed a change in rasp after a few hundred miles? Mine no longer rasp, just the usual upshift "fart" if I catch it at a certain rpm range when the exhaust valves do their thing. I didn't think it would change, but I guess coating the interior exhaust pipes with soot after a few hundred miles did it's thing in a good way.
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      12-12-2019, 08:14 AM   #95
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Quote:
Originally Posted by doughboy View Post
This is why the so called "experts" haven't looked into this.

Because it's just a bit out of their comfort zones. They're not thinking like engineers they're just doing what they always do.
I think from another perspective, this definitely would not be a "bolt-on" system like a traditional mid-pipe, which would be a downer for those who enjoy using the stock muffler and were happy with their AA/VSRF mid-pipes.

I say that because you will need to weld on the pipes to the OE muffler due to the curves needed. Band clamps only work if there aren't bends, space is simply too tight to make it work, unless the aftermarket can figure it out.

Maybe someone will develop a new rear section and have the option to keep the secondary cats or remove them and sell it to the masses?
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      12-12-2019, 08:16 AM   #96
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Quote:
Originally Posted by spool twice View Post
ntg44, have you noticed a change in rasp after a few hundred miles? Mine no longer rasp, just the usual upshift "fart" if I catch it at a certain rpm range when the exhaust valves do their thing. I didn't think it would change, but I guess coating the interior exhaust pipes with soot after a few hundred miles did it's thing in a good way.
3500 RPM rasp is still there. I can't figure it out. But I've also gone through 2 revisions of mufflers and I haven't driven as many miles as you have. It's not that bad though, and is easily manageable with throttle.

Given the circumstances though, since a new exhaust will be developed anyway, I'm not going to invest any more money when the car will most likely have a completely redesigned system in 1-2 months. Just don't see the point in spending any more money and time over it. Winter finally hit Chicago, so won't even be driving the car much until then. I can wait
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      12-12-2019, 09:01 AM   #97
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Yeah I wasn't criticising their business acumen at all. Far from it.

I meant even when you explain how and why you want this odd arrangement they don't understand the physics and try to talk you out of it.

They build exhausts but don't get the physics of them soundwise.
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      12-12-2019, 09:16 AM   #98
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Definitely didn't take it that way, and I fully agree with you. Equal-length is a game changer and the future, it sounds completely different in a positive way.
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      12-13-2019, 02:45 AM   #99
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Quote:
Originally Posted by ntg44 View Post
3500 RPM rasp is still there. I can't figure it out. But I've also gone through 2 revisions of mufflers and I haven't driven as many miles as you have. It's not that bad though, and is easily manageable with throttle.
Have you looked into Helmholtz chambers/resonators? You can tune these to remove a specific range of frequencies. Might be the last little thing you need to perfect the sound? Even better, you can add as many as you need, tuned to different frequency ranges, say if there's a bit of a boom/drone - should be able to completely remove it!
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      12-16-2019, 11:25 PM   #100
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Hey guys.....Spool, ntg, I've been gone for a little bit. I went to Asia after Thanksgiving so I didn't get any of my ideas done.....until today. I completed an equal length dual exit valved exhaust. I'm not sure about the sound yet. But I'll post videos and pics tomorrow. I couldn't stand the way the stock muffler sounded even after all my tweaking, so I got rid of it and fabricated a new rear section.
After a short drive I still don't think it sounds as good as my single exit exhaust, but I guess I'll know more after tomorrow.
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      12-16-2019, 11:43 PM   #101
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Quote:
Originally Posted by RMDZidane View Post
Hey guys.....Spool, ntg, I've been gone for a little bit. I went to Asia after Thanksgiving so I didn't get any of my ideas done.....until today. I completed an equal length dual exit valved exhaust. I'm not sure about the sound yet. But I'll post videos and pics tomorrow. I couldn't stand the way the stock muffler sounded even after all my tweaking, so I got rid of it and fabricated a new rear section.
After a short drive I still don't think it sounds as good as my single exit exhaust, but I guess I'll know more after tomorrow.
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      12-17-2019, 06:12 AM   #102
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Quote:
Originally Posted by RMDZidane View Post
Hey guys.....Spool, ntg, I've been gone for a little bit. I went to Asia after Thanksgiving so I didn't get any of my ideas done.....until today. I completed an equal length dual exit valved exhaust. I'm not sure about the sound yet. But I'll post videos and pics tomorrow. I couldn't stand the way the stock muffler sounded even after all my tweaking, so I got rid of it and fabricated a new rear section.
After a short drive I still don't think it sounds as good as my single exit exhaust, but I guess I'll know more after tomorrow.
Welcome back

Regardless of how it sounds, this will be good to know for R&D purposes. Not sure how much of the thread you've gotten through, but in January, my car is going in for development of a production run exhaust. Your results (along with photos ) would be beneficial to gauge how much merge is necessary to get that desirable tone of your V1 and my V2 system.
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      12-17-2019, 04:04 PM   #103
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Have you guys seen the x force varex mufflers? They have a valve fitted in the muffler. I was initially concerned about them creating a restriction but have seen them fitted on some big hp motors.
I've just made a mock up to the equivalent size of 2 mufflers out of some big fruit tins, when I get time I'm going to see if they fit under the back end.
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      12-17-2019, 07:14 PM   #104
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My results aren't promising. With the valves closed it sounds as anemic as stock. With the valves open it sounds better, but not great. It's certainly not music to my ears. I have to wait for some more free time tonight before uploading a video and a picture showing what I did. A Magnaflow #11386 x-pipe muffler was used to replace the oem unit.

edit:
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      12-18-2019, 12:32 AM   #105
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Here is a video:



Tell me what you think. I'm not a big fan of the sound
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      12-18-2019, 02:26 AM   #106
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I think it sounds pretty good, the smooth I6 sound comes through for sure.

But I'm not a fan of pops & bangs, I mapped them out on my M2comp with BM3.
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      12-18-2019, 03:11 AM   #107
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Quote:
Originally Posted by RMDZidane View Post
Tell me what you think. I'm not a big fan of the sound
To me it sounds a whole lot better than any unequal exhaust. This is something I would run on my own car.
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      12-18-2019, 05:14 AM   #108
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Quote:
Originally Posted by RMDZidane View Post
Here is a video:



Tell me what you think. I'm not a big fan of the sound
Any pics of the system from underneath?
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      12-18-2019, 05:36 AM   #109
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Quote:
Originally Posted by RMDZidane View Post
My results aren't promising. With the valves closed it sounds as anemic as stock. With the valves open it sounds better, but not great. It's certainly not music to my ears. I have to wait for some more free time tonight before uploading a video and a picture showing what I did. A Magnaflow #11386 x-pipe muffler was used to replace the oem unit.

edit:[img]
View post on imgur.com
[/img]

Holy crap that sound is still there!!!! Let me buy it!
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      12-18-2019, 05:48 AM   #110
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Quote:
Originally Posted by RMDZidane View Post
Tell me what you think. I'm not a big fan of the sound
Interesting. I think it's okay, but it kinda falls apart under boost/high load. I think your V1 single exit sounds better though.

Regardless, this is a great development that shows what's possible. This just gets me even more excited for the TopGear project in January
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