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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > Cosmetic and Lighting Modifications (exterior & interior) > Universal Diffuser for Sportline Bumper
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      03-11-2019, 03:10 PM   #1
Alpine_F30
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Universal Diffuser for Sportline Bumper

So I've seen people wrap / plastidip their rear "diffuser" section on the Sportline bumper, but never saw anyone try to retrofit some sort of diffuser 'fins' back there to finish off the look.

IMO without the diffuser fins it looks a little off and better untouched, but after seeing some people in VW community using "Universal Diffusers" on their rear bumpers with good results I figured I'd look for something relevant to the F30. I stumbled across this:

https://www.ebay.com/itm/23-x6-Ikon-...72.m2749.l2648
At 24" wide it fits nicely between the dual exhaust tips and is subtle enough to fit back there without sticking out and looking out of place. Not to mention at $11.99 shipped it was worth a shot. You can also just wrap it (or dip it) with what you use to black out the "diffuser" section/cutout so it really blends in.

Without further adieu, here's how it turned out:




If anyone is interested in exactly how I attached it let me know and I can put up a DIY. Basically it comes with double-sided tape, but you can only use about 1/3 of it because the rest doesn't have anywhere to attach to.

There's a few ways you could do this, and it would definitely be easiest if you took the whole rear bumper off, but I went the lazy route and just used a couple spare brackets laying around from an old HID kit on a previous car, you could definitely find something even better at Home Depot though.

Here the one's I used though for reference, this pic is from an ebay listing actually but it's the exact one's, they're roughly 4.5" long.


I don't have time to do a proper full DIY yet, but a quick couple steps that I used:

1. Jack rear end of car up
2. Mark the center of the diffuser with a piece of tape by measuring the distance between the two exhaust tips.
3. Find the 2 T-15 screws at the bottom of the bumper, right at the edge, they hold the bumper cover up onto some plastic support it seems like. These are where the brackets will get attached, and then the diffuser will use 3M tape to bottom of bumper + the brackets to stay secured (so far so good after 2 weeks )
5. Align diffuser at center of bumper, if you have a spare jack or something to hold it up it will help, and then mark where the brackets line up on the diffuser so you can use those to line up where holes will go into diffuser.
6. Take your diffuser and lay flat, then lay brackets where you marked, find a good place where holes in bracket align with diffuser, I marked 4 total, 2 per bracket, see pic above for where. Because you're doing this sort of blind this isn't perfect, I had to re-drill one of them to get the bracket to align right. You can't see under there at all though, so no biggie to me, but to avoid you'll want to take rear bumper off to make this more accurate.
7. Attach brackets now into rear bumper with T-15's, not super tight, but tight, you may need to adjust them slightly.
8. Peel just the ends of the 3m tape so you can tear off easily when all ready
9. Align diffuser up with bracket holes, doing adjustments where necessary, making sure it aligns with rear of bumper nicely, then attach you nuts/bolts ideally, self tapping screws may work too though it's semi-thick plastic.
10. Once it looks and feels pretty solid, tear off 3m tape, hold in place for a couple minutes, if it's cold maybe apply a little heat.

Last edited by Alpine_F30; 03-19-2019 at 11:46 AM.. Reason: Add link to diffuser on ebay
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      03-11-2019, 03:25 PM   #2
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Looks really good!
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      03-12-2019, 11:25 AM   #3
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      03-13-2019, 08:04 PM   #4
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Nice! Just ordered mine. I think I will sand, prime and paint it myself! Thanks for sharing!
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      03-13-2019, 08:10 PM   #5
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Quote:
Originally Posted by jlorenzo125 View Post
Nice! Just ordered mine. I think I will sand, prime and paint it myself! Thanks for sharing!
Awesome! I'm gonna post up a little DIY here this week with where I drilled holes, the bumper bolts I tapped, and the brackets.

FWIW it comes in a decent looking gloss black, but the edges could benefit from sand/paint. You really don't see it though under there unless you get down real low and close.
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      03-18-2019, 05:40 PM   #6
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Quote:
Originally Posted by Alpine_F30 View Post
Awesome! I'm gonna post up a little DIY here this week with where I drilled holes, the bumper bolts I tapped, and the brackets.

FWIW it comes in a decent looking gloss black, but the edges could benefit from sand/paint. You really don't see it though under there unless you get down real low and close.
Any pics of the type of brackets u used? I'm thinking of going to home depot and looking for something. There's no where on the bumper to attach the rear part of the diffuser without some sort of bracketing indeed ol.
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      03-19-2019, 11:11 AM   #7
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Quote:
Originally Posted by jlorenzo125 View Post
Any pics of the type of brackets u used? I'm thinking of going to home depot and looking for something. There's no where on the bumper to attach the rear part of the diffuser without some sort of bracketing indeed ol.

Posting up pics of bracket now to original post, although I think you could probably find something even better at home depot.
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      03-19-2019, 11:54 AM   #8
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Quote:
Originally Posted by Alpine_F30 View Post
Posting up pics of bracket now to original post, although I think you could probably find something even better at home depot.
Thanks!
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      03-19-2019, 02:51 PM   #9
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I went to home depot and got some brackets along with some nuts and bolts to secure them into holes i drilled into the rear part of the 'diffuser'. Worked really well, also used some thicker double sided tape to secure the edges up along bottom of bumper. Came out pretty good!
---Sorry for the dirty car, its been raining for a week now




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Last edited by jlorenzo125; 03-23-2019 at 07:06 AM..
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      03-19-2019, 03:04 PM   #10
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Quote:
Originally Posted by jlorenzo125 View Post
I went to home depot and got some brackets along with some screws and washers to secure them into holes i drill into the rear part of the 'diffuser'. Worked really well, also used some thicker double sided tape to secure the edges up along bottom of bumper. Came out pretty good!
---Sorry for the dirty car, its been raining for a week now
Oh sick dude, that was fast, nice work!

I was a little worried that it wouldn't be strong enough with only those 2 brackets, would like a 3rd on the far right, but it still feels really sturdy. I guess it's just a small piece of plastic that needs to stay in place.
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      03-19-2019, 03:14 PM   #11
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Quote:
Originally Posted by Alpine_F30 View Post
Oh sick dude, that was fast, nice work!

I was a little worried that it wouldn't be strong enough with only those 2 brackets, would like a 3rd on the far right, but it still feels really sturdy. I guess it's just a small piece of plastic that needs to stay in place.
Thanks! And I think what would be good to try is have a buddy drive behind ur / my car to see if the diffuser flops or wiggles at all during driving, especially at highway speeds Probably would a little who knows
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      03-19-2019, 05:39 PM   #12
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Quote:
Originally Posted by jlorenzo125 View Post
Thanks! And I think what would be good to try is have a buddy drive behind ur / my car to see if the diffuser flops or wiggles at all during driving, especially at highway speeds Probably would a little who knows
Ha, yeah I was thinking the same, and also get them to take some rollers while you're at it
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