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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Thoughts on fabricating my own custom downpipes with wastegate dump.



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      09-04-2014, 08:37 AM   #1
elijahcole92
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Thoughts on fabricating my own custom downpipes with wastegate dump.

Hello all,

Found a few threads discussing the desire for some people to have the violent sound that comes from having an external wastegate dump to atmosphere. Having owned multiple Evos, and Stis with external wastegate setups, i SEVERELY miss being loud and obnoxious. (As does my fiance ) However, i know without extensive modification, external wastegates are not an option on our stock frame turbos.

My idea is to use the stock turbo/wastegate setup, but instead customize my downpipes similar to that of the Evo/Sti setup. Here are some links to what their exhaust housing/downpipes look like.

http://www.google.com/search?q=evo+o...F%3B1000%3B662

http://www.google.com/search?q=06+st...es%3B500%3B500

Now here is a ROUGH sketch on paint of what i was considering.



Here is also a picture of a stock turbo turbine housing..



I would just simply make a divider inside the 3" downpipes i currently have and run the wastegate side into a separate 1.25" pipe that would be just like any normal wastegate dump tube.

I'd love to hear you thoughts/suggestions/corrections/advice. I have experience with aluminum metal working, but not as much with SS, so it will be a slight learning experience.
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      09-04-2014, 09:34 AM   #2
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Wont be as efficient, if it was they would've already been made, you'd want aftermarket waste gates on before wanting something like this, which not many will do either. Just got single turbo w/external gate and will be much better results. Had the open gate on my brothers STI and didn't see much gain over reg/downpipe
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      09-04-2014, 12:47 PM   #3
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It's efficient on both the Evo and Sti platforms even when backpressure is not an issue. The cars are able to hold boost easier in the higher rpms and i've personally seen back-to-back testing that shows a slight increase in spoolup. I'm not really doing it for the power gain though, mostly for sound, and the fact that i just like being unique and fabricating my own parts
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      09-04-2014, 01:01 PM   #4
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I've done it in the past on other cars and made custom plates like that weld the downpipe to. We just waterjet them. But how will you control boost? I'm a bit unfamiliar as to how you'll get the DME to control an aftermarket wastegate. I guess same way single turbo guys do?
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      09-04-2014, 01:28 PM   #5
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Good luck
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      09-04-2014, 01:47 PM   #6
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Maybe my first post wasn't clear enough. My design will not be changing/removing/installing ANY kind of wastegate. This type of setup uses the stock wastegate. All it does is separate the two exhaust gases instead of letting them merge into a single collector downpipe. The wastegate gas will go straight to atmosphere like an external wastegate atmospheric dump tube. The regular exhaust gas will procede normally into the downpipe out the exhaust.
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      09-04-2014, 02:06 PM   #7
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I see. But how will you actually separate the exhaust being dumped from the exhaust going to downpipe? The Evo turbo already has a divorced wastegate so it's easy to keep separate. The N54 turbo's wastegate feeds back into the exhaust before the downpipe bolts up. Unless you separate them, you'd basically have an open exhaust since you'll dump a good portion of both the wastegate exhaust and regular.

I do love the way an open dump wastegate sounds, I just don't see how it would work on the stock turbo.
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      09-04-2014, 02:16 PM   #8
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Shadow, did you take a look at both of the links i posted? On the Subaru downpipe, it simply has a dividing wall between the wastegate and turbine side. I would make something similar.

The divided would stick out of the downpipe, like the subaru one so that the wastegate gases don't actualy have a chance to merge instead are forced into one half of the downpipe that then goes into a straight dump tube.
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      09-04-2014, 02:17 PM   #9
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I am wondering though, (should probably email Terry about this) is if this would affect my o2 readings at all?

I wouldn't think so just because the exhaust gas, whether coming past the turbine or the wastegate will havethe same a/f ratio.
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      09-04-2014, 04:29 PM   #10
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Iwas looking for a option like this

Im thinking the easiest way would be to have a set of downpipes already and cut out a piece of the pipe closest to the v-band ring and then weld in two flat pieces of metal to basically patch it back and of course the actual wastegate pipe

Will take a lot of test fitting you might be able to get away with doing just one turbo since its so tight
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      09-04-2014, 05:23 PM   #11
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I did see that. I guess I'm just having a hard time seeing how to divide it in the space there. The sti turbo is pretty straight forward. Ours looks like less space and deeper.

But good luck, I'm curious to see how it turns out.
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      09-04-2014, 07:12 PM   #12
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Yeah i think it will take some test fitting, i might be upgrading to RBs sometime so i might just wait until then, unless i finish this turbo honda project and have a DD for a little while so the BMW can sit on the lift for a while haha.

335byi - This is exactly what i'm planning! If only i had the measurements to know how deep and such to make the divider piece
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      09-04-2014, 11:42 PM   #13
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No way to seal the wastegate outlet, it'll leak at idle/cruise
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      09-05-2014, 03:35 AM   #14
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Every attempt at that type of dump pipe that I've seen on EVERY platform, sounds terrible (like it has a leak because it DOES have a leak). It especially won't work on an N54 because the wastegate is often open off boost.
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      09-05-2014, 09:29 AM   #15
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Why is the wastegate open at idle/cruise? Well, your opinion is noted and that's why many would rather recirculate their wastegate dump. However, many others like the loud "leak"
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      09-06-2014, 05:49 AM   #16
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Quote:
Originally Posted by Tiago@VRSF View Post
No way to seal the wastegate outlet, it'll leak at idle/cruise
Just weld it shut?

I'm sure I've seen this done on a standard turbo before. and it would be good on our turbos due to stupid waste gate rattle.
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      09-06-2014, 07:08 AM   #17
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Quote:
Originally Posted by elijahcole92
Why is the wastegate open at idle/cruise? Well, your opinion is noted and that's why many would rather recirculate their wastegate dump. However, many others like the loud "leak"
Vacuum actuated rather than boost actuated (so normally open rather than normally closed) iirc

Is a safety feature.. If the wastegates failed say, they'd stay open so nothing breaks
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      09-07-2014, 07:54 AM   #18
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Ahh, i gotcha. Well it may be a small leak then..

You can't weld the wastegate shut without adding external wastegates, which is not what i'm doing. My plan is to utilize the stock internal wastegate configuration.
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      09-08-2014, 10:01 AM   #19
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Look into trying a boost activated exhaust cutout instead.
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      10-13-2014, 09:07 AM   #20
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Anyone have a used/damaged stock turbo or turbo hotside i could use for fab/mock up purposes?!
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      10-21-2014, 06:09 PM   #21
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Update: Got one downpipe fabbed up, second one half way done! Had to remove the motor mount to get them in and out though -_-

Hopefully i'll have some pics and startup tonight
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      10-21-2014, 06:34 PM   #22
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Quote:
Originally Posted by elijahcole92 View Post
Update: Got one downpipe fabbed up, second one half way done! Had to remove the motor mount to get them in and out though -_-

Hopefully i'll have some pics and startup tonight
Nice! Keep us updated. Definately a cool project and interesting idea
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