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Thread: Anyone running a 4" Exhaust?

  1. #1
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    Anyone running a 4" Exhaust?

    So I am going to have a exhaust built soon and was curious should I run a 3.5" or a 4" exhaust?

    I currently have a 3.5" DP and a 6765dbb TS 1.15 Turbo PW66mm WG ..

    I was looking into a 4" vibrant resonator with a vibrant 1155 muffler

    http://www.ebay.com/itm/Vibrant-1155...59e0f4&vxp=mtr

    has anyone ran one of these?

    I ran the 3" version of the resonator and muffler on my old NA e36 m3 and loved it.
    2002 911 Turbo k16 billet, JIC Coilovers, GT3BBK, Cobb Mafless, Oz Ultra

  2. #2
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    I have a 4" straight pipe on my 2.8

    [ame]http://www.youtube.com/watch?v=PZnDWSk4XGo[/ame]

    Ground clearance sucks. I scrape the V-bands all the time.

    -Mike
    IG: @mikevanshellenbeck

  3. #3
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    I run 4 inch exaust with two borla racing mufflers here is a vid:


    [ame]http://youtu.be/xB83loAfsaU[/ame]
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  4. #4
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    Quote Originally Posted by MikeE36 View Post
    I have a 4" straight pipe on my 2.8


    Ground clearance sucks. I scrape the V-bands all the time.

    -Mike
    Sounds nice i would run a straight 4" but cali cops are no joke..

    have you thought about a oval 4" where it scrapes? might help a bit..
    2002 911 Turbo k16 billet, JIC Coilovers, GT3BBK, Cobb Mafless, Oz Ultra

  5. #5
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    In the process of building a complete 4 inch oval exhaust now. Hope to be done by 1/1/13.

  6. #6
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    Last edited by BenFenner; 12-03-2012 at 09:55 AM.

  7. #7
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    Quote Originally Posted by DADx2 View Post
    In the process of building a complete 4 inch oval exhaust now. Hope to be done by 1/1/13.
    I'd see some pics. Where are you sourcing the oval tubing. Btw, doesn't oval pipe flow less than circular?

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  8. #8
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    One of my bigger mods planned for the new year is I want a 3.5-4" exhaust....worried if I can keep the sounds down with 4" but I foresee big gains over my current 3"..decisions!

  9. #9
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    I'm sure there is power to be had but... I made over 630 with a 3" down pipe, 3" exhaust, magnaflow resonator and dynomax vt muffler. My exhaust is far from perfect. it looks like a shitty muffler shop welded it up. It's not pretty or ideal and it supports decent whp.
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  10. #10
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    I know why someone with an 8 second 1/4 mile car has a 4" but it doesn't make a lot of sense for the rest of us.
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  11. #11
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    Quote Originally Posted by futureroadracer View Post
    I'm sure there is power to be had but... I made over 630 with a 3" down pipe, 3" exhaust, magnaflow resonator and dynomax vt muffler. My exhaust is far from perfect. it looks like a shitty muffler shop welded it up. It's not pretty or ideal and it supports decent whp.
    Oh I'm sure many (you're the perfect example!) made damn good power on a 3" exhaust..the idea of a few extra ponies and earlier spool (I'm just a wee 2.8L)makes the idea of a bigger exhaust an attractive one for me.

  12. #12
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    Hey boris, why are you running mufflers at all? Your car seems pretty much drag only, wouldnt the mufflers detract from the awesome noise and add a little (if insignificant) amount of weight?

  13. #13
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    Quote Originally Posted by e30kid89 View Post
    Oh I'm sure many (you're the perfect example!) made damn good power on a 3" exhaust..the idea of a few extra ponies and earlier spool (I'm just a wee 2.8L)makes the idea of a bigger exhaust an attractive one for me.
    Believe me, I want it too. Just not sure if the minimal difference in spool and slight HP gain is worth fitting a huge exhaust under the car. Especially if it's louder and scrapes on every bump.

    I think there have been significant gains made in the Supra world although I remain skeptical... I don't think I'd see a 50-100whp gain (suggested on the supra forums) if I went to a 3.5-4" exhaust. Maybe though...
    OLD
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    1/4 mile: 10.91@144.38
    http://www.youtube.com/watch?v=L_f7fUVqblI

    NEW BUILD
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    635wtq
    120.51mph trap speed




  14. #14
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    Quote Originally Posted by RobertFontaine View Post
    I know why someone with an 8 second 1/4 mile car has a 4" but it doesn't make a lot of sense for the rest of us.
    When early spool as possible is one of the goals for the system, generally the larger the exhaust the better to a point.

    For an SC, sure. You NEVER get good spool regardless of exhaust choice

    -Mike
    IG: @mikevanshellenbeck

  15. #15
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    Quote Originally Posted by MikeE36 View Post
    When early spool as possible is one of the goals for the system, generally the larger the exhaust the better to a point.

    For an SC, sure. You NEVER get good spool regardless of exhaust choice

    -Mike
    lmao!

  16. #16
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    Quote Originally Posted by DADx2 View Post
    In the process of building a complete 4 inch oval exhaust now. Hope to be done by 1/1/13.
    A little math for fun...

    Area of a circle: pi × r2 with pi = 3.141593
    Area of an oval: pi x L x W


    4" circular exhaust diameter =12.566 in2
    4" oval exhaust (~2.75" tall and 4.375 wide) =9.449 in2
    Circle = ~33% bigger
    (12.566 - 9.449 = 3.117 / 9.449 = answer, if I understand correctly. )


    3.5" circle = 9.621 in2
    3.5" oval (~2.5"L and 4"W) = 7.854 in2
    So, circle = ~22.5% bigger

    Continued:
    4" oval is ~1.82% smaller than 3.5" circle.
    4" oval is ~33.67% bigger than 3" circle
    For reference, a 3" circle is 7.069 in2.

    More fun - 4" circle is ~77.76% bigger than a 3" circle.
    All things to keep in mind when making a decision on exhaust size.


    So, if I were to build and exhaust, then I would definitely go for a 4" exhaust if possible. Also, I definitely would not go from a 3" circular exhaust to a 3.5" oval exhaust because it is only ~11.1% bigger.
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  17. #17
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    Quote Originally Posted by BadBoostedBmwM3 View Post
    I'd see some pics. Where are you sourcing the oval tubing. Btw, doesn't oval pipe flow less than circular?

    Sent from my iPhone 5 using BF.com
    I'm getting my stuff from Spintech (mufflers and tubing) I'm planning on doing a thread on it as soon as I get a little farther along with the fabbing.

    I assume it may not flow AS good as round, but better than my 3 inch is good enough for me.

    Quote Originally Posted by BadBoostedBmwM3 View Post

    4" oval is ~1.82% smaller than 3.5" circle.
    4" oval is ~33.67% bigger than 3" circle (Great information)
    For reference, a 3" circle is 7.069 in2.

    More fun - 4" circle is ~77.76% bigger than a 3" circle.
    All things to keep in mind when making a decision on exhaust size.


    So, if I were to build and exhaust, then I would definitely go for a 4" exhaust if possible. Also, I definitely would not go from a 3" circular exhaust to a 3.5" oval exhaust because it is only ~11.1% bigger.
    Thanks for the math. Great information there !!!!

    My initial intent for going oval was due to clearance issues with my 3 inch. My V-band clamp took one helluva beating due to my car being low. And since my goal was ground clearance, 4 inch oval seemed to be the only sensible choice. So.... with that being said, I will be gaining a 33.67% bigger exhaust AND gaining ground clearance.

    Several months ago, I found a couple good articles (Supra stuff IIRC) talking about considerable whp/wtq increases when increasing exhaust size. IE from 3 inch to 3.5. As with anything, there are multiple variables. I should have some results pretty soon. My last dyno was 598/516 and I am changing ONLY the exhaust, so the comparison will be apples to (bigger) apples .

  18. #18
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    Quote Originally Posted by BadBoostedBmwM3 View Post
    A little math for fun...

    Area of a circle: pi × r2 with pi = 3.141593
    Area of an oval: pi x L x W


    4" circular exhaust diameter =12.566 in2
    4" oval exhaust (~2.75" tall and 4.375 wide) =9.449 in2
    Circle = ~33% bigger
    (12.566 - 9.449 = 3.117 / 9.449 = answer, if I understand correctly. )


    3.5" circle = 9.621 in2
    3.5" oval (~2.5"L and 4"W) = 7.854 in2
    So, circle = ~22.5% bigger

    Continued:
    4" oval is ~1.82% smaller than 3.5" circle.
    4" oval is ~33.67% bigger than 3" circle
    For reference, a 3" circle is 7.069 in2.

    More fun - 4" circle is ~77.76% bigger than a 3" circle.
    All things to keep in mind when making a decision on exhaust size.


    So, if I were to build and exhaust, then I would definitely go for a 4" exhaust if possible. Also, I definitely would not go from a 3" circular exhaust to a 3.5" oval exhaust because it is only ~11.1% bigger.
    Once you see and work with oval exhaust pipe, you will understand it is not really oval and actually much closer to rectangular. There is much less loss of area than what you suggest.

  19. #19
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    Holy math dump...... thanks for the info brother!

  20. #20
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    Quote Originally Posted by pbonsalb View Post

    Once you see and work with oval exhaust pipe, you will understand it is not really oval and actually much closer to rectangular. There is much less loss of area than what you suggest.
    Actually. I tend to agree with you. I was looking at some oval tubing online, and it looked very rectangular.
    Hence. I used the best numbers for oval pipe I found. I'd really be interested in seeing some actual numbers.

    My numbers were more so for fun. Either way, the circular measurements should apply though.

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  21. #21
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    I has a sewer pipe.
    This space for rent.

  22. #22
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    I have 5" down and 4" under and back whit 1 large muffer on my E34 turbo.
    Nice sound and 89db whit DB testing on track


  23. #23
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    Quote Originally Posted by Mister v12 View Post
    I have 5" down and 4" under and back whit 1 large muffer on my E34 turbo.
    Duramax?

  24. #24
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    Quote Originally Posted by MTrace View Post
    Duramax?
    He he

    No, bmw V12 and BIG turbo.
    1200whp at 2 bar so i need it

    Last edited by Mister v12; 12-04-2012 at 01:47 AM.

  25. #25
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    Quote Originally Posted by Mister v12 View Post
    He he

    No, bmw V12 and BIG turbo.
    1200whp at 2 bar so i need it

    2002 911 Turbo k16 billet, JIC Coilovers, GT3BBK, Cobb Mafless, Oz Ultra

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