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      03-22-2017, 10:16 PM   #1
n55jb4
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Rear bumper diffuser DIY?

I have a single side exhaust 328 diffuser like in the first picture, but I would like to convert exhaust for a dual side 335 style. To fit second set of tips (passenger side), I will need to modify diffuser - it's a plastic, not CF. So I was thinking is it possible to cut out a second arch in it so it will look descent and without breaking plastic? I'm only thinking about this DIY because this little plastic cosmetic part costs $300
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      03-22-2017, 10:46 PM   #2
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Of course it's possible but it will take skill. It's not something I would be able to do.
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      03-22-2017, 10:57 PM   #3
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With the small lip above the opening on the bumper, you'd need to cut the bumper with a Dremel, smooth it, add Bondo, form it to the look of the opposite side, smooth it more, paint it, and blend. Even then, it wouldn't be perfect. With the amount time and effort required to do that well, you'd be wishing you bought the diffuser in the end.
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      03-22-2017, 11:30 PM   #4
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Quote:
Originally Posted by Welcome to NBA Jam View Post
With the small lip above the opening on the bumper, you'd need to cut the bumper with a Dremel, smooth it, add Bondo, form it to the look of the opposite side, smooth it more, paint it, and blend. Even then, it wouldn't be perfect. With the amount time and effort required to do that well, you'd be wishing you bought the diffuser in the end.
+1

Compared to what is required for a DIY the $300 would be well worth it....now if you take it to a shop, hmm not sure but probably still better to buy the new one and try and sell your current diffuser on the classifieds here, help with some of the cost there
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      03-22-2017, 11:45 PM   #5
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Car looks great with the single side exhaust. Why butcher it?
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      03-22-2017, 11:57 PM   #6
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Point taken! Will sell my diffuser and buy new one
I agree it's not necessary as it looks good enough with single side exhaust, but a mod bug bit me recently so I have to do something haha
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      03-23-2017, 12:14 AM   #7
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So n55jb4, you have a 328? This mod isn't worth it. You're sweating the $300 trim but the exhaust modifications are going to set you back more than that.
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      03-23-2017, 12:51 AM   #8
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Quote:
Originally Posted by absentmathis View Post
So n55jb4, you have a 328? This mod isn't worth it. You're sweating the $300 trim but the exhaust modifications are going to set you back more than that.
I agree, but it's just for looks, I'm not changing full exhaust. I will only add a second set of tips behind the muffler or may go with dual single tips 335 style
The cost of this mod is roughly $80 for welding work and cost of nice tips
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      03-23-2017, 01:00 AM   #9
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Quote:
Originally Posted by n55jb4 View Post
I agree, but it's just for looks, I'm not changing full exhaust. I will only add a second set of tips behind the muffler or may go with dual single tips 335 style
The cost of this mod is roughly $80 for welding work and cost of nice tips
Seems silly. Did you have an n55 at one point?
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      03-23-2017, 02:32 AM   #10
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Quote:
Originally Posted by absentmathis View Post
Seems silly. Did you have an n55 at one point?
Nope, I only have 328, but I may sell it and buy 335 in the future.

Maybe it's silly, but isn't all modding? We do it for hobby, it's certainly not necessity If you mean you don't like the looks of double side setup - I can understand that, but I like it.

How about this then:
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      03-23-2017, 03:29 AM   #11
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I personally have never been a fan of dual exhausts tips on each side as shown in the second pic in your original post, looks silly, very 80's in my opinion. The pic above of the 335 exhaust looks good. Though if you want the 335 exhaust on your 328, you need the 335 trunk pan, trunk liner, exhaust heat shield and additional hangers. Then there's is the exhaust itself.
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      03-23-2017, 04:19 AM   #12
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Your exhaust is going to look quite funny when it's cold out...
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      03-23-2017, 05:16 AM   #13
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Quote:
Originally Posted by Manual Transmission View Post
Your exhaust is going to look quite funny when it's cold out...
That's pretty funny, but in all honesty it'll look like a stock 335i w/o the golf tee mod...
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      03-23-2017, 08:17 AM   #14
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Quote:
Originally Posted by BdSM n54iS View Post
That's pretty funny, but in all honesty it'll look like a stock 335i w/o the golf tee mod...
The money is better spent on the 330i intake mod, +25 hp and with a chip tune, at least +10 hp more.
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      03-23-2017, 08:21 AM   #15
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Quote:
Originally Posted by Manual Transmission View Post
Your exhaust is going to look quite funny when it's cold out...
There will be a pipe welded to a muffler, so that is taken care of I hope you didn't assume I'm going to weld a fake tip to a under-body?
I'm frankly surprised how many people here don't know this mod. This was one time very popular one
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      03-23-2017, 08:23 AM   #16
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Quote:
Originally Posted by Bluewater328iT View Post
The money is better spent on the 330i intake mod, +25 hp and with a chip tune, at least +10 hp more.
Intake mod? You mean 3SI (3 stage intake)? BMW modded that for me. Right on the factory. They call it n51
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      03-23-2017, 08:24 AM   #17
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Quote:
Originally Posted by n55jb4 View Post
Intake mod? You mean 3SI (3 stage intake)? BMW modded that for me. Right on the factory. They call it n51
Yep, then you already have it.
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      03-23-2017, 08:29 AM   #18
n55jb4
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Guys, apparently we are stuck somewhere in 2007 early forum days
We can do better than that

P.S. or maybe my join date confuses good people here. I'm on forum since 2011 actually and this is my 3rd iteration. I got it - you naturally think I'm an idiot and noob, but cut me some slack, I'm not that bad really

Come on guys and gals, this mod was a hit in good old times - don't you remember? My issue is with diffuser mainly, these were not common in old days

Last edited by n55jb4; 03-23-2017 at 08:35 AM.
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      03-23-2017, 08:33 AM   #19
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Just don't do it.
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      03-23-2017, 08:36 AM   #20
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Quote:
Originally Posted by Wolf 335 View Post
Just don't do it.
Why? The last picture I posted - doesn't it look good?
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      03-23-2017, 08:54 AM   #21
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Quote:
Originally Posted by n55jb4 View Post
Why? The last picture I posted - doesn't it look good?
In the pic you posted it is doable because there is no lip around the hole. And yes it does look good.

The one he wants has a lip around the hole, and to cut his and replicate lip properly will take some effort which may add up to the cost of a new replacement diffuser.
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      03-23-2017, 09:02 AM   #22
n55jb4
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Quote:
Originally Posted by Wolf 335 View Post
In the pic you posted it is doable because there is no lip around the hole. And yes it does look good.

The one he wants has a lip around the hole, and to cut his and replicate lip properly will take some effort which may add up to the cost of a new replacement diffuser.
Oh I got ya. I guess him - is me. I posted previously (post #6 in this thread) that I am going to sell my diffuser and buy a new one. People don't like to read long boring threads - can't blame them. However, thanks for liking that pic - at least I know now that people like it and that is the way to go
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