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Back pressure in exhaust system - what to do to prevent this?

Discussion in 'A3/S3 Forum (8L Chassis)' started by DJ_Troopa, Jan 3, 2012.

  1. DJ_Troopa
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    DJ_Troopa K1 Driver

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    [Jan 3, 2012]
    Hi guys

    I've been thinking recently about my exhaust system and how much back pressure it has. If i put my foot down and let off when the turbo spools, i get that back pressure sound when i let off like it's just throwing it out.

    Basically my system is, 200 cell sport cat, centre box, then straight pipe going to my tailpipes, no backbox. I believe having no backbox is creating the back pressure. Am i right? I've been reading up on back pressure, and i don't know if it's a good or bad thing? But then i think big companies such as Milltek don't do that so mine must be done incorrectly? How can i resolve mine without having to fork out for a Milltek system? Can i simply add a normal small bacbox and it will be better?

    Thanks

    Ajay
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  3. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 3, 2012]
    Thats not back pressure... with your setup you have very little if any back pressure...

    <tuffty/>
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  4. Prawn
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    Prawn My other car is a MINI!!!!

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    [Jan 3, 2012]
    what do you mean 'that back pressure sound' mate?

    I hate to suggest it, but it sounds like your describing the sound of your DV!
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  5. DJ_Troopa
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    DJ_Troopa K1 Driver

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    [Jan 3, 2012]
    Thanks Paul

    Do you know what it might be then? It's always done that since i had the exhaust done a couple years ago and that's why i thought it was back pressure? Very hard to give an example but here you go........ 'vroooooooooom WOAW!' Vroom is when foot is down and it spools and then WOAW is when i let off like it's throwing the gases out of the exhaust in 1 big bunch. :laugh:
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  6. DJ_Troopa
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    DJ_Troopa K1 Driver

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    [Jan 3, 2012]
    It's 100% coming out of the exhaust tailpipes and always done this since i had the system done.
    #5
  7. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 3, 2012]
    Mine does that... thats not back pressure... normally does it if I let off just after the turbo spools and about to come on song... sounds normal to me

    <tuffty/>
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  8. DJ_Troopa
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    DJ_Troopa K1 Driver

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    [Jan 3, 2012]
    Yup that's exactly what mine sounds like. From my cat i have a 3" pipe which goes to the centre box, then after the centre box the pipework is reduced to 2.5". Could that be why it makes that sound?
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  9. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 3, 2012]
    Mines 3" all the way to the Milltek back box and does it... even when I had a small straight though back box it did it... its normal mate..

    <tuffty/>
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  10. BENJAMIN
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    BENJAMIN Active Member

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    [Jan 3, 2012]
    Mine also does this under the same circumstances as tufty mentioned, I was under the impression it was the waste gate opening, bypassing the turbo and creating a sudden increase in noise in the exhaust.
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  11. superkarl
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    superkarl MAN OF STEEL

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    [Jan 3, 2012]
    It's just the resonant noise. A HUGE complex back box would reduce it like the oem one. You'd have loads of back pressure tho. On turbo cars the clearer the path for exhaust gases the better.

    I'm interested in yiur system mate, tell us more, start a thread lol
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  12. DJ_Troopa
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    DJ_Troopa K1 Driver

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    [Jan 4, 2012]
    Have you got a pic of your system? The people who done my Longlife system said they couldn't do a 3" pipe because it was too big? And also towards where the backbox should be, they've shaped the pipe to go down and then up again! You know when you're behind an Evo and you see the pipe which goes down towards the floor and up again? Mine looks like that but other S3's i see don't have that!
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  13. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 4, 2012]
    Loads in my build thread... but here is a taster..
    [​IMG]

    <tuffty/>
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  14. DJ_Troopa
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    DJ_Troopa K1 Driver

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    [Jan 4, 2012]
    Whoa that backbox is huge! Is that a Milltek? Also have you got a decat?

    Here's an old pic of mine but you can see the exhaust going down underneath if you know what i mean? .....................

    [​IMG]
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  15. superkarl
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    superkarl MAN OF STEEL

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    [Jan 4, 2012]
    They have to go down a bit to clear the rear subframe where the haldex is held. you can still see it on tufftys. That's why the oem system has a squashed section of pipe here, to clear the frame but also so it doesnt hang Low.

    I wouldn't worry, its pretty much inline with the wheels so shouldnt give you clearance issues.
    Unless your on a road with some insane camber.
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  16. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jan 4, 2012]
    Yes its a milltek... got pissed off with the drone in the car with the original setup...
    [​IMG]

    Mine goes under the subframe fine and not scraped in on anything yet...
    [​IMG]

    <tuffty/>
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  17. Teji
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    Teji New Member

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    [Jan 10, 2012]
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