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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N55 Turbo Engine Tuning and Exhaust Modifications - 335i Tuning > Exhaust mod in N55 E92 after DP



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      04-06-2014, 08:29 AM   #1
MNick
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Exhaust mod in N55 E92 after DP

What are the performance gains between muffler mod vs cat back vs axle back vs stock with golf tee mod in a car with cattless DP???

The stock E92 2.25" x 2 piping has little resistance and I'd hate to spend $1,200~2,500 on exhaust, get only 2whp and have pull me over/ricer loud exhaust.

I know I'm asking a lot, but it would help people figure out the utility/value of an exhaust mod or upgrade…
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      04-06-2014, 09:40 AM   #2
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Negligible gains across the board. Only the downpipe will provide decent gains.
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      04-06-2014, 01:29 PM   #3
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I had a Pro turner in my area tell me it was worth slapping a high flow system on before having him dyno & tune the car… I doubt he has seen the exhaust setup on the N55 e92, but I wanted to see what the consensus was.

I agree that gains are likely trivial.
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      04-06-2014, 07:03 PM   #4
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I'm curious also if anyone else can chime in on these gains or lack thereof. More out of curiosity than anything. While DP are guranted for me I've been toying with the idea of the VRSF catback exhaust.
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      04-06-2014, 08:16 PM   #5
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Just use the search function or google. The stock Catback is already perfectly free-flowing.
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      04-08-2014, 10:22 PM   #6
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Quote:
Originally Posted by Sidewinderpb View Post
Just use the search function or google. The stock Catback is already perfectly free-flowing.

I searched for more specific data (actually dyno #'s results) to no avail.

Please let me know or post the URL if you find any dyno results comparing e92 N55 with cattless DP stock exhaust (or golf tee mod) to upgraded exhaust…
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Last edited by MNick; 04-08-2014 at 10:26 PM. Reason: reduce redundancy
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      04-08-2014, 10:43 PM   #7
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That's because nobody wants to pay money to throw their car on the dyno twice, just to see the same numbers each time.

Let me just throw up a disclaimer before I break it down for you:

I am not an engineer; nor have I ever aspired to become one. I am also not a BMW guru; just an enthusiast.

That being said - the reason that you see noticeable gains when replacing the downpipe, is that you are removing a restrictive catalytic converter. Doing so, allows the exhaust to flow much more freely - thus the gains.

When replacing the already free-flowing stock catback, with and equally (slightly more) free-flowing aftermarket catback - you are not really removing anything restrictive. Hence, you will see negligible gains.
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Last edited by Sidewinderpb; 04-08-2014 at 10:59 PM.
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      04-09-2014, 07:21 AM   #8
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Quote:
Originally Posted by Sidewinderpb View Post
That's because nobody wants to pay money to throw their car on the dyno twice, just to see the same numbers each time.

Let me just throw up a disclaimer before I break it down for you:

I am not an engineer; nor have I ever aspired to become one. I am also not a BMW guru; just an enthusiast.

That being said - the reason that you see noticeable gains when replacing the downpipe, is that you are removing a restrictive catalytic converter. Doing so, allows the exhaust to flow much more freely - thus the gains.

When replacing the already free-flowing stock catback, with and equally (slightly more) free-flowing aftermarket catback - you are not really removing anything restrictive. Hence, you will see negligible gains.
Exactly, I can't see there being much resistance over the distance from DP to exhaust tips (with that muffler mod) enough to add up and restrict the turbo and necessitate the upgrade (2.5" pipes for $1K-3K).

I figured I was asking a lot to see data, I certainly don't want to pay for research (multiple dyno runs).
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      04-09-2014, 08:31 AM   #9
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Quote:
Originally Posted by MNick View Post
Exactly, I can't see there being much resistance over the distance from DP to exhaust tips (with that muffler mod) enough to add up and restrict the turbo and necessitate the upgrade (2.5" pipes for $1K-3K).

I figured I was asking a lot to see data, I certainly don't want to pay for research (multiple dyno runs).
Yeah, BMW already nailed it with the catback. Upgrading will only provide a different tone to the exhaust - which is still awesome.

I also believe that the stock piping is already 2.5".
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      04-18-2014, 07:53 AM   #10
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Quote:
Originally Posted by Sidewinderpb View Post
Yeah, BMW already nailed it with the catback. Upgrading will only provide a different tone to the exhaust - which is still awesome.

I also believe that the stock piping is already 2.5".
Yeah I measured it a while ago looked like 2.25" but you might be right.
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      04-18-2014, 07:57 AM   #11
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Quote:
Originally Posted by MNick View Post
I had a Pro turner in my area tell me it was worth slapping a high flow system on before having him dyno & tune the car… I doubt he has seen the exhaust setup on the N55 e92, but I wanted to see what the consensus was.

I agree that gains are likely trivial.
Let me guess, he is the one selling it to you?
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      04-21-2014, 08:05 PM   #12
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Quote:
Originally Posted by divisionbell77 View Post
Let me guess, he is the one selling it to you?
LOL! I was waiting for it, but he did not try to sell one to me (don't think they stock them)... He did talk me into stopping by the shop later this week to see the single turbo upgrade they r putting into a N54, hope to see it on the Dyno... More interested in this than an exhaust.
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      04-21-2014, 10:36 PM   #13
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I think the biggest restraint is from the turbo. If the outlet is 3 inches what good would it be to have anything larger. Behind the turbo? You might lose back pressure and power. I'd stick with stock unless we run bigger outlet turbos. Of course you might want the benefit of sound which has it's perks!
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      04-22-2014, 08:07 AM   #14
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Quote:
Originally Posted by marCOCOpuffs View Post
I think the biggest restraint is from the turbo. If the outlet is 3 inches what good would it be to have anything larger. Behind the turbo? You might lose back pressure and power. I'd stick with stock unless we run bigger outlet turbos. Of course you might want the benefit of sound which has it's perks!
If backpressure = power then we would all be running around with 1" exhausts. A low pressure area will help suck air out from a high pressure area. Read up on an expansion valve. It isn't going to help a lot having a larger DP, but it definitely isn't going to hurt performance like you say. Turbo cars run best with an open downpipe. You are correct that the biggest restriction is the turbo.
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      04-22-2014, 01:45 PM   #15
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based on the options you gave I'm gunna have to say very small gains from all options except the dp which i believe has some decent gain?
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      04-22-2014, 03:02 PM   #16
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Quote:
Originally Posted by Sidewinderpb View Post
Negligible gains across the board. Only the downpipe will provide decent gains.
This.

In forced induction engines, exhaust gasses are just that. Contrast with natural aspiration, wherein a certain amount of backpressure is beneficial (I don't know more than that, I've always had a turbo'd engine).

The premier method of getting rid of exhaust gasses? I'm glad you asked:


Any piping just creates drag that slows down your turbine. Larger piping creates less drag; straighter piping creates less drag; etc.
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