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[Alloytec] VZ SV6 - exhaust rear pipe

Discussion in 'V6 Development And Modification' started by newjack, May 19, 2015.

  1. newjack

    newjack Member

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    Hi everyone,
    Before all the '6 will never sound like an 8', 'dumbass p-plater' etc etc..

    I know with the catback centre and rear pipes you should run a 2.5" pipe at largest due to the back pressure,

    Wondering if it's possible to run a REAR PIPE of the catback with a 3" straight pipe (all joined onto 2.5" centre x pipe with mufflers to dual high flow cats etc into headers..) without losing too much overall power.

    Car- VZ SV6 (190kw) 3.6L alloytec

    Thanks
    J
     
  2. EYY

    EYY Well-Known Member

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    Use a single 2 1/2 rear section with a resonator. Without a resonator, a v6 commodore will always sound pretty shocking and obnoxious.
     
  3. newjack

    newjack Member

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    I don't mind it being obnoxious since in everyone else's eyes we are already labeled as a ########.. Just the look on the old peoples faces **** me up the wall. Government brainwashed to live in society a certain way. So I say to them f ya if you don't like it.

    I have it currently on a 2.5" rear pipe with a resonator. Was thinking 2.5" or 3" rear pipe without the resonator
     
  4. Sandman

    Sandman Challenge Accepted

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    Don't do it. It will sound like ****. Mine had no rear muffler when I bought it, droned like a motherfkr and sounded just generally bloody horrible. But if that's what you want I guess then go for it.
     
  5. Kiddo

    Kiddo You're serious bro?!

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    Stick with a 2.5", WITH resonators/mufflers.

    It's not about being obnoxious because everyone thinks you are (Which you are if you give in). It's because without them, the sound waves will cause a resonance within the cabin, making it a horrible place to be. I've been in the back seat of a vehicle that droned so bad, i felt physically ill. Seriously.

    NAAF actually makes a catback system almost exactly to the original one you described! So I would personally get one off him :)
     
  6. newjack

    newjack Member

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    Had a fairly droney vx where my interior parts would vibrate a fair bit. Loved every second of it (had it for two years).
    Thanks fellas for the replies, I appreciate it!
     
  7. commodore665

    commodore665 expat Saffa

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    When I had a Ecotec ,I put on a 2.5 inch cat back and headers , at idle nice and burbly , and throttle , not so much , I'm resisting the urge to upgrade the zorst opn the SV6, but might go for some dual tips for the looks only .
     
  8. EYY

    EYY Well-Known Member

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    Don't be part of the reason that p platers have a bad reputation. It ruins it for the rest of us that tastefully modify cars by making the media, and the public generalise that all 'car guys' are inconsiderate and selfish.
     
  9. Sandman

    Sandman Challenge Accepted

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    These days I have the stock system with a resonator where the rear muffler would be. Not too loud but has a little bit of a note to it, so sounds ok.
     
  10. bob builder

    bob builder Member

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    when i was 17 i thought a straight 6 with a twin system sounded good, emu export tasted awesome and oysters were shite.
    I have since changed my opinion on the above.
    cant put an old head on young shoulders,everyone has a turn at that if you live long enough.

    its simple,
    you either want the noise more than the power (3" cat back)
    or the power more than the noise (less than 3")
     
  11. commodore665

    commodore665 expat Saffa

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    With age comes wisdom , I still think oysters taste like snot , can't say on emu export though
     
  12. newjack

    newjack Member

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    Would the half inch difference in pipe diameter [ 2.5" compared to 3" ] have a fairly noticeable difference in regards to the overall amount of how loud it would be?

    Thanks..
     
  13. Capsule

    Capsule Member

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    0.5" of difference in diameter = 2.1 square inch of difference in surface. Multiply that by the length of the tube and you get the point.
     
  14. MattK

    MattK New Member

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    Hmmmm , droning !
    Yes , one grows tired of it very quickly ..
    Your car might sound fantastic and loud on the outside , but not so good on the inside ( Wont be too long before your looking for a convenient power pole to slam into @ 100kmh to end the droning )
    My VL droned VIA the Boot , and I was doing everything possible to get it to stop ..
    More carpeting in the boot , and I even built a firewall behind the back seats to stop sound getting into the cabin .
    I never got rid of the droning 100% , now I despise loud exhausts . ( Just give me a quiet car )
    Sure put on headers , and free up the exhaust flow - but quietly ... ( young people - so noisy )
     
  15. Not_An_Abba_Fan

    Not_An_Abba_Fan Exhaust Guru

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    It's not about back pressure. You don't want back pressure at all, it's bad. You need velocity without compromising flow.

    You need to move the gas as fast as possible, not as much as possible. The exhaust system in itself is actually just there to make the car quiet and to get the gas out the back of the car. This is just to comply with legislation, nothing else. Engineers have designed the system as best they can to be quiet and flow well enough to meet legislative requirements.

    The first thing people think when changing an exhaust is bigger is better, or I need to make it louder. There are lots of off the shelf systems that do this and improve performance. The performance improvement is gained by removing the restrictive exhaust. The other problem with exhausts, and this is the one that makes the biggest difference, is that you will not get an exhaust that will perform to it's maximum capabilities in all rev ranges. Fluid dynamics makes that impossible. The infinite change in velocity and flow and pulse spacings in an exhaust through all driving conditions makes tuning an exhaust impossible on a street car.

    The best systems will improve mid to top end but will always sacrifice bottom end. The way to do this is have it flowing well out of the engine, then through the pipe diameter and muffler design, try not to slow it down too much before it reaches the tail pipe.

    Now, after having said all that, as mentioned, I do a system that probably is one of the better velocity exhaust systems for the alloytec, it is 2 1/4" off the cats and goes through two small straight through mufflers before merging into a single 3" and out through a 3" resonator. It is nice and deep, doesn't drone, and keeps the speed of the gas going because of the merge.

    As exhaust cools down, it takes up less space, so to keep it moving, you need to do one or both of two things. Reduce pipe diameter and/or merge the pulses so they aid in velocity. Larger V8 engines don't require the same tolerances in an exhaust because they have the capacity to keep the gas flowing. A small 3.6L V6 doesn't, so it needs all the help it can get.
     
  16. newjack

    newjack Member

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    Thanks for your indepth response abba fan!
    Ended up with a full xforce setup.. 1 5/8 headers out 2 1/2 into dual 200cpi 2 1/2 high flow cats into 2 1/2 centre single muffler into a 2 1/2 rear pipe with a hotdog.
    ----
    Side note; is there much difference running a rear hotdog over a rear straight through pipe?
    I was told the hotdog removes the old man fart noise and gives it a better note? Does it reduce the loudness noticeably?

    Thanks fellas
     
  17. Not_An_Abba_Fan

    Not_An_Abba_Fan Exhaust Guru

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    Bet it sounds loud and raspy now.
     
  18. newjack

    newjack Member

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    Not An Abba Fan

    is there much difference running a rear hotdog over a rear straight through pipe?
    I was told the hotdog removes the old man fart noise and gives it a better note? Does it reduce the loudness noticeably?
     
  19. Not_An_Abba_Fan

    Not_An_Abba_Fan Exhaust Guru

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    A hotdog is just a small resonator. Yes, it helps with reducing the raspy note. Without it, it will be louder.

    The larger the body of any muffler/resonator, the quieter and deeper it will sound.
     

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