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      10-06-2020, 09:14 AM   #1
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Exhaust details & undercarriage look from G82 M4 / G80 M3

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Looking underneath the car I noticed that the exhaust is quite different from the other S58s, you can see a small central resonator (red circle), 2 secondary catalysts/OPFs (blue) and 2 primary catalysts (yellow), but the curve of the tubes and the location of the catalysts it totally different from the X3/4M. I'm surprised to see the primary catalysts so far from the manifolds, any thoughts?

Name:  G80 M3 G82 M4 Exhaust System Undercarriage Underbody.jpg
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This is the X3/4M exhaust

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      10-06-2020, 09:47 AM   #2
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Preproduction maybe? I'm not an exhaust expert, but I imagine having the primary cats far from the manifold isn't good for efficiency.
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      10-06-2020, 09:57 AM   #3
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Hmmmm, interesting. I wonder if it is an attempt at making an equal length exhaust system.
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      10-06-2020, 10:30 AM   #4
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does that make it easier to de-cat
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      10-06-2020, 10:36 AM   #5
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Interesting!
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      10-06-2020, 11:54 AM   #6
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Routing the downpipe under the transmission is very strange to me. It almost looks like the M5 midpipe setup. I wonder if they are planning for a V engine configuration down the road. I know that sounds farfetched but I do not see why else they would do it this way.
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      10-06-2020, 02:34 PM   #7
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Quote:
Originally Posted by CanAutM3 View Post
Hmmmm, interesting. I wonder if it is an attempt at making an equal length exhaust system.
This was my initial thought as well... maybe they've seen all the work the F8x folks were doing with EL systems and tried to implement it
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      10-06-2020, 02:43 PM   #8
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Looks like after-market exhaust suppliers will just need to tap in aft of item #9, which means much less metal/shorter piping than was required for the F80/82/83. Hopefully, that will translate into a less expensive exhaust mod.
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      10-06-2020, 04:44 PM   #9
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Quote:
Originally Posted by CanAutM3 View Post
Hmmmm, interesting. I wonder if it is an attempt at making an equal length exhaust system.
Looks like the opposite. Notice the significant extra length as they pipe 3 cylinders to the other side of the gearbox. Going for the Subaru warble. :
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      10-06-2020, 04:47 PM   #10
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Quote:
Originally Posted by NISFAN View Post
Looks like the opposite. Notice the significant extra length as they pipe 3 cylinders to the other side of the gearbox. Going for the Subaru warble. :
It depends which of the two manifolds goes through the longer route: the front or the rear one.

On the F8X, the exhaust gases of front manifold have to travel a longer distance that the ones of the rear manifold. Making a detour for the rear manifold balances the exhaust length.
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      10-06-2020, 04:55 PM   #11
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Quote:
Originally Posted by CanAutM3 View Post
Quote:
Originally Posted by NISFAN View Post
Looks like the opposite. Notice the significant extra length as they pipe 3 cylinders to the other side of the gearbox. Going for the Subaru warble. :
It depends which of the two manifolds goes through the longer route: the front or the rear one.

On the F8X, the exhaust gases of front manifold have to travel a longer distance that the ones of the rear manifold. Making a detour for the rear manifold balances the exhaust length.
Yes I realise that, but not to the extent shown here. This looks deliberately out of balance.

Twin turbo straight sixes are not new, here is a picture of an RB26DETT front pipe to balance the lengths. You are talking 12" max to make up.
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      10-06-2020, 05:04 PM   #12
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Quote:
Originally Posted by kyleb350 View Post
Preproduction maybe? I'm not an exhaust expert, but I imagine having the primary cats far from the manifold isn't good for efficiency.
The distance does nothing to efficiency. It just adds time, and therefore emissions, to the cold start. Once at operating temp in a few seconds the efficiency will be the same.
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      10-06-2020, 05:17 PM   #13
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Can anyone explain what is going on in the original picture? The car looks like it is participating in some sort of circus trapeze act.

Just curious...
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      10-06-2020, 05:19 PM   #14
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Enables a lower profile of the exhaust resulting in less drag of the fast flowing under car air? Might not be enough space when routed one side to achieve the same?
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      10-06-2020, 05:21 PM   #15
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I think BMW ran out of room to put both primary cats on one side ... so they used the unused space on the other side of the transmission for one of the cats and piped under transmission to that space.
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      10-06-2020, 05:21 PM   #16
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Quote:
Originally Posted by Pinkoboe View Post
Can anyone explain what is going on in the original picture? The car looks like it is participating in some sort of circus trapeze act.

Just curious...
they lowered it from a helicopter for a PR stunt.
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      10-06-2020, 05:46 PM   #17
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Principles of thermal dynamics says largest temp difference from intake to exhaust mani equals largest power. Placing them closest to the manifold will equal more heat but to be honest I don't think that logic was used here looks like packaging but I didn't design the car. Also cats like to be heated up to function properly maybe the idea is to get into them and keep them heated. Or the all most important topic BMW topic NVH, BMW has started to make these M3/4 everyday cars with minimal NVH it's possible moving the cats closer helps eliminate some NVH topic the car tuners (me included) will remove those NVH nannies anyways!
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      10-06-2020, 06:06 PM   #18
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Quote:
Originally Posted by NISFAN View Post
Yes I realise that, but not to the extent shown here. This looks deliberately out of balance.

Twin turbo straight sixes are not new, here is a picture of an RB26DETT front pipe to balance the lengths. You are talking 12" max to make up.
See below aftermarket solutions for the F8X. They do add a fair bit of length.
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      10-06-2020, 06:53 PM   #19
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https://g80.bimmerpost.com/forums/sh....php?t=1763157

In this Youtube video filmed by a german YouTuber, a BMW M employee states at around 8:20, that the exhaust and sound design team specifically engineered the exhaust to be equally lengthened to create the desired sound profile for the new BMW M3/M4. These undercarriage photos seem to confirm that.
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      10-06-2020, 07:07 PM   #20
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Quote:
Originally Posted by tbraden View Post
In this Youtube video filmed by a german YouTuber a BMW M employee states at around 8:20, that the exhaust and sound design team specifically engineered the exhaust to be equally lengthened to create the desired sound profile for the new BMW M3/M4. These undercarriage photos seem to confirm that.
for sharing this video. It's the most informative video I've watched about the G8X, finally something technical :
  • Base: 1.3bar boost
  • Comp: 1.7bar boost
  • 5.5kg of sound-deadening removed over the base 3-series
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Last edited by CanAutM3; 10-06-2020 at 07:59 PM..
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      10-06-2020, 07:09 PM   #21
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Quote:
Originally Posted by M-SP0RT View Post
does that make it easier to de-cat
I hope so and to put back the cats when it goes in for service...plug and play
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      10-06-2020, 07:45 PM   #22
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Could it be in the yellow circles those are braided exhaust pipes?
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