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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > Photo/Video/Media Gallery > DIY Aggresive rear Diffuser



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      05-07-2018, 10:17 PM   #1
Evochuck
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DIY Aggresive rear Diffuser

Been working on a diffuser for my e90 LCI 335.
With my aeronautical background and the fact that I have access to most materials for pretty cheap I decided to try my hand at this.

Essentially, I am trying to reduce the parachute effect of the rear bumper, while at the same time improving the look of the car.

This is the test car


First Side slat tryout (all mockups are made with corrugated plastic)



I guess it worked out okay, least gave me something to work with, I then got busy with the middle part



Mockup slats ''glued'' in place




Testing on the car





Finished ish product
Basically, the front of the plate attaches to the flat part between the LCAs and the curves are ment to stay close but not touch the exhaust pipes, the entire Diffuser maintains about 3/4 inch clearance with the OEM exhaust (PE in my case)



I got busy with CATIA and crew the entire base plate, I then cut/shaped the plate at work.

I was hesitant between bedliner coating and wrap it in CF, I had the CF, decided to go with that.

Here is the end result





Now I need to decide on my Fin profile, I decided I didnt like the one I did initially, I am REALLY OPEN to any ideas or suggestions, looking to do 4 fins on the plate (larger space in the middle) and one under each side.

Here is another one I mocked up (excuse the mess)


Last edited by Evochuck; 07-31-2018 at 02:10 PM..
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      05-07-2018, 10:19 PM   #2
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Cool custom build!
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      05-07-2018, 11:30 PM   #3
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Some pics arent working
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      05-08-2018, 12:20 AM   #4
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^ Last two pictures aren't visible.

Cool idea I like the finished product. What kind of testing are you going to do to see what difference it makes?

I worked on the underbody/diffuser subsection for my school sae team, learned a lot about the impacts of the diffuser on performance. I'm curious as to how you decided the dimensions and placements of pretty much everything on it. Is it just a random mockup or is it influenced by your aeronautical background?
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      05-08-2018, 01:29 AM   #5
Thate90
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Looks good so far would like to see how the final product turns out. If it turns out the way I think it could would you be willing to make one for me at all? I only ask cause I have the same car and model as you
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      05-08-2018, 07:07 AM   #6
Evochuck
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Quote:
Originally Posted by Nafy View Post
Cool custom build!
Thanks! Looking forward to finishing it!

Quote:
Originally Posted by balxoscar View Post
^ Last two pictures aren't visible.

Cool idea I like the finished product. What kind of testing are you going to do to see what difference it makes?

I worked on the underbody/diffuser subsection for my school sae team, learned a lot about the impacts of the diffuser on performance. I'm curious as to how you decided the dimensions and placements of pretty much everything on it. Is it just a random mockup or is it influenced by your aeronautical background?
Ill be 100% honest with you, the main objective was to remove the rear bumper parachute effect, any other effect is just a perk, Seeing as the plate is a lot smoother than the undercarriage, I would expect undercar turbulence to go down as well as increase negative pressure. When it comes down to the fins, Ill be honest, I have no idea what I'm doing
My aeronautical background mostly helped me drawing it and fabbing it up.
If I had access to more equipment I would have done the large bend with a much larger radius to smooth out the airflow.

Quote:
Originally Posted by Thate90 View Post
Looks good so far would like to see how the final product turns out. If it turns out the way I think it could would you be willing to make one for me at all? I only ask cause I have the same car and model as you
Let's start by seeing how bad it will look at the end and perhaps I could start looking into that afterwards, I am located in Canada as well and the main piece is pretty massive, shipping will suck.


Sill looking for Ideas for the fins!
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      05-08-2018, 08:21 AM   #7
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nice work
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      05-08-2018, 10:38 AM   #8
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Need to see the last 2 pics!!
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      05-08-2018, 11:08 AM   #9
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Quote:
Originally Posted by cpie168 View Post
Need to see the last 2 pics!!
Tried fixing the links, hopefully that works!
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      05-08-2018, 12:37 PM   #10
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Looks good now! But need to see it installed on the car. Good job!
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      05-08-2018, 01:19 PM   #11
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I'm interested in hearing more about the parachute effect you're referencing. Assuming you're talking about air from forward motion being caught up in the bumper, how much are we really talking about here? This seems like something that would have a pretty big effect on performance and fuel efficiency, I would assume the Bavarian engineers would have minimized this as much as possible, without compromising looks.

Also, the 335is comes stock with a finned rear diffuser. I am now wondering if they made this change to later models based on the same issue you're tackling now?
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      05-08-2018, 09:00 PM   #12
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Quote:
Originally Posted by b92 View Post
I'm interested in hearing more about the parachute effect you're referencing. Assuming you're talking about air from forward motion being caught up in the bumper, how much are we really talking about here? This seems like something that would have a pretty big effect on performance and fuel efficiency, I would assume the Bavarian engineers would have minimized this as much as possible, without compromising looks.

Also, the 335is comes stock with a finned rear diffuser. I am now wondering if they made this change to later models based on the same issue you're tackling now?
How bad is it? not sure at all, I wouldn't be surprised if it didn't have to do with cost cutting, take a look at a tesla rear end, obviously no mufflers helps....
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      05-08-2018, 09:03 PM   #13
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I'm REALLY digging the FancyWide diffuser, unfortunately, it is not as funtional and well, they don't make them from the 335, but I might take inspiration for the sides!



Made a bit of progress tonight, mocked up the side pieces, these will be one piece with two bends.



Also test fitted the center piece to the car, seems like if I want it to stick out a bit I will have to fab another small piece to connect to the frame, its all part of the RnD process I guess. I will also have to unbend the piece a bit so it does not touch the mufflers, as this would probably be insanely noisy if left as is.




Last edited by Evochuck; 05-09-2018 at 09:24 AM..
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      05-09-2018, 09:42 PM   #14
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Side pieces were made today, managed to wrap one up to now, they take forever to wrap.....





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      05-10-2018, 07:39 AM   #15
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Wow, pretty cool project.
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      07-31-2018, 02:08 PM   #16
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Here is the mostly completed product, I might add slats between the fins under the muffler tips but ill run like that for a while.



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