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      12-05-2011, 01:49 PM   #1
MDORPHN
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Restricted cat-back?

A well known N54 tuner has told me that an aftermarket cat-back exhaust will help the 1M gain top end power.

According to him, both the 135i and 1M share a restricted section of cat-back compared to the 335i and 535i.

Typically, cat-back systems yield relatively minor power gains (though they often produce much nicer sounds).

Has anybody compared the cat-back sections of 135i/1M relative to the 335i/535i?

Thanks.

Neil
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      12-05-2011, 03:29 PM   #2
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Quote:
Originally Posted by MDORPHN View Post
A well known N54 tuner has told me that an aftermarket cat-back exhaust will help the 1M gain top end power.

According to him, both the 135i and 1M share a restricted section of cat-back compared to the 335i and 535i.

Typically, cat-back systems yield relatively minor power gains (though they often produce much nicer sounds).

Has anybody compared the cat-back sections of 135i/1M relative to the 335i/535i?

Thanks.

Neil
On the stock pipe, you can see a restriction just aft of the connecting flange (downstream from the resonator). When COBB had my car on the dyno a couple weeks ago, they indicated that this part of the stock cat-back appeared to be causing a small issue and would likely be improved with an aftermarket cat-back. I understand that significant gains are more likely to come from the downpipes and cat area, but I've ordered an Eisenmann cat-back and will see if that makes a difference and, if so, exactly how much.
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      12-05-2011, 03:45 PM   #3
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Quote:
Originally Posted by Texas F1 View Post
On the stock pipe, you can see a restriction just aft of the connecting flange (downstream from the resonator). When COBB had my car on the dyno a couple weeks ago, they indicated that this part of the stock cat-back appeared to be causing a small issue and would likely be improved with an aftermarket cat-back. I understand that significant gains are more likely to come from the downpipes and cat area, but I've ordered an Eisenmann cat-back and will see if that makes a difference and, if so, exactly how much.
Do you know whether a mid-pipe -- either stock off a N55-powered 135i or the Berk Technology piece -- would eliminate this restriction?

Thanks.

Neil
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      12-05-2011, 03:46 PM   #4
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Quote:
Originally Posted by MDORPHN View Post
Do you know whether a mid-pipe -- either stock off a N55-powered 135i or the Berk Technology piece -- would eliminate this restriction?

Thanks.

Neil
Yes. You can see it here:

http://www.1addicts.com/forums/showt...php?p=10917176
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      12-05-2011, 03:51 PM   #5
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Thanks, but I'm still not sure I've correctly identified the constricted area.

Neil
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      12-05-2011, 03:56 PM   #6
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Quote:
Originally Posted by MDORPHN View Post
Thanks, but I'm still not sure I've correctly identified the constricted area.

Neil
Do you see the exhaust on the right? It has those 2 big fat cats in the middle. Those are the restrictive part because they are the secondary cats.

The exhaust on the left which is the Berk does not have those. All it has are 2 small long resonators to make sure you don't get drone. Cats are extremely restrictive and resonator's aren't.
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      12-05-2011, 03:59 PM   #7
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It was unclear to me that Texas F1 --- and Cobb Tuning -- was referring to the secondary cats or some crimp in the tubing.

If the former (the cats), easy to address with an N55 or Berk Tech midpipe.

Neil
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      12-05-2011, 07:30 PM   #8
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Quote:
Originally Posted by MDORPHN View Post
It was unclear to me that Texas F1 --- and Cobb Tuning -- was referring to the secondary cats or some crimp in the tubing.

If the former (the cats), easy to address with an N55 or Berk Tech midpipe.

Neil
Neil, no, I'm not referring to the cats. What I was trying to describe earlier is what appears to be a restriction in the stock exhaust pipe immediately downstream from the flange where the cat-back portion connects to the secondary cat and resonator section. If you look at the diagram of the stock exhaust that Nate posted on the other thread, it's just past the dashed line that separates the portions of the system. It's hard to see from the diagram, but it is noticeable when you look at the actual pipe.
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      12-05-2011, 08:56 PM   #9
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Quote:
Originally Posted by Texas F1 View Post
Neil, no, I'm not referring to the cats. What I was trying to describe earlier is what appears to be a restriction in the stock exhaust pipe immediately downstream from the flange where the cat-back portion connects to the secondary cat and resonator section. If you look at the diagram of the stock exhaust that Nate posted on the other thread, it's just past the dashed line that separates the portions of the system. It's hard to see from the diagram, but it is noticeable when you look at the actual pipe.
OK, I suspected that you would have referred specifically to the secondary cats if that was your concern.

Since the constriction is behind both the secondary cats and the resonator, it would be the rearmost section of the exhaust -- entailing the single pipe running to the muffler -- that would need to be replaced in order to "free-up" the system.

Neil
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      12-06-2011, 11:02 AM   #10
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Quote:
Originally Posted by MDORPHN View Post
OK, I suspected that you would have referred specifically to the secondary cats if that was your concern.

Since the constriction is behind both the secondary cats and the resonator, it would be the rearmost section of the exhaust -- entailing the single pipe running to the muffler -- that would need to be replaced in order to "free-up" the system.

Neil
I will just comment that everything I have read and heard indicates the mid pipe with its secondary cats is far more restrictive than the rear section. Keep researching.
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