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M2 Technical Topics > N55 Engine / Drivetrain / Exhaust / Bolt-ons / Tuning > M2 Exhaust vs. MPE Exhaust

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      09-08-2016, 11:13 AM   #1
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M2 Exhaust vs. MPE Exhaust

This question is based solely on looking at pictures, so anyone that has installed an MPE please chime in.

Yes, there might be less baffling or material in the muffler, etc.

But I'm wondering if the majority of the sound gains are resulting from the delete of the center silencer? Seems like a simpler and less expensive mod than gutting the muffler.

Thoughts?
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      09-09-2016, 02:37 AM   #2
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The exhaust flow in MPE can bypass the muffler with electrically controlled valves opened, I believe that's what makes the difference.

Akrapovic uses an identical muffler design but only mates it to a split dual pipe configuration to pursue a better flow capacity in the middle section at the cost of the high velocity of the hot air coming out of downpipe, of which I really doubt the gain outweigh the loss, HP/Torque wise.
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      09-09-2016, 08:20 PM   #3
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Quote:
Originally Posted by SeanWRT View Post
The exhaust flow in MPE can bypass the muffler with electrically controlled valves opened, I believe that's what makes the difference.

Akrapovic uses an identical muffler design but only mates it to a split dual pipe configuration to pursue a better flow capacity in the middle section at the cost of the high velocity of the hot air coming out of downpipe, of which I really doubt the gain outweigh the loss, HP/Torque wise.
Are you saying that the single pipe design is better than the dual pipe? I was wondering this the other day.
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      09-09-2016, 08:26 PM   #4
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Quote:
Originally Posted by OrangeCrush
Quote:
Originally Posted by SeanWRT View Post
The exhaust flow in MPE can bypass the muffler with electrically controlled valves opened, I believe that's what makes the difference.

Akrapovic uses an identical muffler design but only mates it to a split dual pipe configuration to pursue a better flow capacity in the middle section at the cost of the high velocity of the hot air coming out of downpipe, of which I really doubt the gain outweigh the loss, HP/Torque wise.
Are you saying that the single pipe design is better than the dual pipe? I was wondering this the other day.
I am saying, to make most efficient AND biggest power THROUGHOUT the band, you will want the smallest diameter pipe (and thus the highest velocity) that can support the maximum exhaust flow the engine is able to make.

The Dual pipe diameter may be more than enough to support m2 stock flow. Only my speculation though.
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      09-09-2016, 09:27 PM   #5
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So if back pressure is reduced. Is the velocity also reduced?
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      09-09-2016, 09:30 PM   #6
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Quote:
Originally Posted by SeanWRT View Post
The exhaust flow in MPE can bypass the muffler with electrically controlled valves opened, I believe that's what makes the difference.

Akrapovic uses an identical muffler design but only mates it to a split dual pipe configuration to pursue a better flow capacity in the middle section at the cost of the high velocity of the hot air coming out of downpipe, of which I really doubt the gain outweigh the loss, HP/Torque wise.
Isn't the stock exhaust also allowing some exhaust to bypass? Or is it only providing a second exit path after?
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      09-09-2016, 09:50 PM   #7
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Quote:
Originally Posted by masou
Quote:
Originally Posted by SeanWRT View Post
The exhaust flow in MPE can bypass the muffler with electrically controlled valves opened, I believe that's what makes the difference.

Akrapovic uses an identical muffler design but only mates it to a split dual pipe configuration to pursue a better flow capacity in the middle section at the cost of the high velocity of the hot air coming out of downpipe, of which I really doubt the gain outweigh the loss, HP/Torque wise.
Isn't the stock exhaust also allowing some exhaust to bypass? Or is it only providing a second exit path after?
Stock mid pipe routes the flow completely into muffler. The flow only travels thru less or no fiber inside of muffler when valves opened.
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      09-09-2016, 09:54 PM   #8
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Quote:
Originally Posted by masou
So if back pressure is reduced. Is the velocity also reduced?
Only by enlarging pipe dia to decrease back pressure should you have a reduced velocity. That's physics.

In most of other cases - removing cats, smoothing passages, etc, the velocity increase. That's why you have more power in the first place - flow gets out quicker.
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      09-09-2016, 10:02 PM   #9
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The real question I am having here, is whether BMW cheaps out on m2 exhaust by not using a dual system, or m2 power level just don't have that flow for a dual to support.

And what is the dia of Akrapovic dual pipes? Down pipe outlet is 3.5" so the combination of the dual shouldn't be larger than that, which is why it doesn't make much sense to me in the first place.

Someone enlightens me or gives some real world before and after please. Until that, Akrapovic is a merely sound mod with no hp loss at best.
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      09-10-2016, 09:08 AM   #10
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Found one reason for a twin pipe design...

http://www.supersprint.com/ww-en/wha...gn-system.aspx

1. ability to increase velocity and still have cats
2. ability to design out droning

Maybe Akrapovic's found using two pipes allowed them to better tune the sound?
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