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Downpipe 3" or 2.5"

Discussion in 'A3/S3 Forum (8L Chassis)' started by Tim_Attard, May 21, 2013.

  1. Tim_Attard
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    Tim_Attard Active Member

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    [May 21, 2013]
    Hi,

    looking at getting a downpipe for my ko3s looking at the £100 ones on ebay and they have 3" or 2.5" i know 3" will be better for flow etc but from what ive seen on here a few people have had problems with it knocking and rubbing etc and had to change engine mounts which i dont want to have to do tbh, so just looking for a bit of advice either go for 2.5 and avoid any knocking or bit ethe bullet and get 3" and run the risk of having to replace engine mounts. is there really that big of a diffrence?

    only going to go stage 1 in the future cant see myself going stage 2
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  3. IrishDave
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    IrishDave Active Member

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    [May 21, 2013]
    Seen as you have a K03 turbo your car is FWD and therefore there is no prop shaft for the downpipe to interfere with so you should not have clearance issues.
    #2
  4. Tim_Attard
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    Tim_Attard Active Member

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    [May 21, 2013]
    is it just the prop that it rubs on nothing else? as im pretty sure some people with the same car expereinced it
    #3
  5. IrishDave
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    IrishDave Active Member

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    [May 21, 2013]
    I could be wrong, but with no prop there you should have all the room in the world to make minor adjustments.
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  6. Grale1
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    Grale1 Member

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    [May 21, 2013]
    I get a knock on my car I have a 3" on a k03 but that from where I took the centre section off and it didn't fix back in it two mounting points the same as they came out. Go 3" all the way IMO
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  7. ANDYTQ
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    ANDYTQ Well-Known Member

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    [May 22, 2013]
    Had a 2 1/2 " custom one on my old one ,you wont need any bigger with a ko3,it made such a difference over the standand system , i cut the old one up to see the internal size ,shocked at how restrictive it was.Mated mine to a s3 milltek and it worked really well with ko3s ,fmic ,intake etc.
    #6
  8. Tim_Attard
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    Tim_Attard Active Member

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    [May 22, 2013]
    hmm ok im gonna see what bore my cat back is and just get one to match as long as its bigger than 2.5
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  9. JudderMan
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    JudderMan Active Member

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    [May 22, 2013]
    I asked this a few months ago and the general consensus was a 3"DP. I haven't fitted mine yet but got a decat too. I'm getting a reducer and a TDi centre section soon (less restrictive), then running it through the OEM rear section. In total mine will cost me around £150. I like bargains and a Milltek cat back would add £360+ to that, and isn't a bargain in my eyes.

    My 2p.
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  10. Tim_Attard
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    Tim_Attard Active Member

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    [May 22, 2013]
    let me know how you get on fitting it, as we have the exact same car :) you doing it yourself?

    also how the hell do you get 37mpg
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  11. JudderMan
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    JudderMan Active Member

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    [May 22, 2013]
    I've been banned from doing/spending anything on the car until after my wedding in August but yeah, I'll be doing it myself (September the 1st ;)) and then getting it mapped. I've been told (on here) that I could see a solid 220bhp/250lbft which is plenty for the money spent.

    37mpg is just pootling around with the odd blast. I don't commute and always get it warm first, always check the tyre pressures, try and stay away from traffic and cruise. On the A69 back from Carlisle to Newcastle I was stuck behind 10 cars/trucks and it was a constant 45mph which saw 45mpg. I run Vpower Nitro with the odd BP Ultimate if I can't find a Shell garage. TBF using the DIS current mpg I have seen what the car is best/most efficient and drive in that style.
    #10
  12. 16Klappe
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    16Klappe RacecaR forward is RacecaR backwards. Supporter

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    [May 22, 2013]
    3", the decat then drops to 2.5 and then down to 2.25. You can't go 3" all the way without some serious issues, it doesn't clear the rear beam without some seriously skilled pipe work. There is nothing fully 3" on the market.

    There are 3" downpipe and reducer decats on eBay for less than £80. Get one bought.
    Last edited: May 22, 2013
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  13. Tim_Attard
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    Tim_Attard Active Member

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    [May 22, 2013]
    fair enough i average 27 but i only ever really use it to do a 10mil trip to and from work as soon as i go for a long journey etc it goes up.

    right so i have gone and messured my cat back and its 2.5 from what i can see so if i got the decats off eBay that go to 2.5 then 2.25 how to i join them up to the cat back as i want to do it myself and don't have easy access to welding
    #12
  14. JudderMan
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    JudderMan Active Member

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    [May 22, 2013]
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  15. Tim_Attard
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    Tim_Attard Active Member

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    [May 22, 2013]
    whats the benifit of the mid section?

    so if i was to get this
    3" 2 1/2" Stainless Steel Exhaust Reducer Pipe T304 | eBay
    all i need is two u bolts and clamp it down

    also another question is with the ebay down pipe assuming its best to get oem gaskets for the turbo to down pipe but what about the gasket to join the decat?
    #14
  16. 16Klappe
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    16Klappe RacecaR forward is RacecaR backwards. Supporter

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    [May 22, 2013]
    Timbo.

    Ignore everyone other than me. If your current centre section and cat are standard you don't need any sleeves or pipes or joins or any other ****.

    Buy this. http://item.mobileweb.ebay.co.uk/viewitem?itemId=400309040920&index=1&nav=SEARCH&nid=76085111727

    Buy a new exhaust clamp and some paste as well as new turbo studs and nuts, setup your angle grinder with a cutting disc. Remove the old downpipe and replace any studs which come out with the turbo studs. Fit the downpipe and slide the decat under your existing exhaust and trim the original centre section if needed. Tighten up the new clamp. It should take less than an hour and a half, all gaskets and bolts are supplied with the downpipe and decat.

    Be happy.
    #15
  17. Tim_Attard
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    Tim_Attard Active Member

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    [May 22, 2013]
    my down pipe and cat are stock, but from the cat on its custom so i have a resonated center and back box etc which is 2.5" i believe
    so would i not need some sort of joiner to slot the end of the decat which is 2.25? to my cat back which is 2.5?

    so my shopping list

    DP & Decat - AUDI A3 1.8T 150HP TURBO EXHAUST DECAT DOWN PIPE 12/96-06/03 DP7928 | eBay
    Paste - 120g EXHAUST ASSEMBLY PASTE SILENCER JOINER GASKET LIKE HOLTS GUN GUM FIRE PUTTY | eBay
    U Clamp - Exhaust U Hose Clamp Clamps Clamping Clips Nuts Bolts Zinc Plated Universal New | eBay (What size would i need?)

    p.s. thanks for helping
    #16
  18. 16Klappe
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    16Klappe RacecaR forward is RacecaR backwards. Supporter

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    [May 22, 2013]
    Yes. Buy it all now.

    IF your centre section is 2.5" then buy a single piece of 2.5" flared exhaust tube and cut the decat at the first ridge to make it 2.5". The Jetex pipes are very good -

    http://item.mobileweb.ebay.co.uk/viewitem?itemId=370814596560&index=6&nav=SEARCH&nid=55056488676

    Slot the flared end over the decat and then fit whatever is bringing your stock up to 2.5" on the end of it once it has been trimmed to suit.

    If you went out to the car, jacked one side up and took a picture for me then all would become clear. But as neither you, nor I or anybody else knows what your custom exhaust is made up of none of us can comment past what has been said.
    Last edited: May 22, 2013
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  19. Tim_Attard
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    Tim_Attard Active Member

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    [May 22, 2013]
    i have to wait till pay day :/ got holiday money to save first :(

    still not sure on how im joing a 2.25 to a 2.5 bore with out a joiner tho :/

    regarding the bolts can i not just re-use the ones that come out the DP?
    #18
  20. 16Klappe
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    16Klappe RacecaR forward is RacecaR backwards. Supporter

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    [May 22, 2013]
    You have obviously already got whatever is needed because your stock cat will have to step up to the centre section IF it is 2.5 as you say.

    Go take a picture of it.
    #19
  21. Tim_Attard
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    Tim_Attard Active Member

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    [May 22, 2013]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    assuming there the section u wanted to see?
    #20
  22. Tim_Attard
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    Tim_Attard Active Member

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    [May 22, 2013]
    ah your edit makes sense ha im a bit slow so need things spelt out as you have probably guessed, i will get that pipe u linked to looks good
    #21
  23. 16Klappe
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    16Klappe RacecaR forward is RacecaR backwards. Supporter

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    [May 22, 2013]
    Stock exhaust, 2.25".
    #22
  24. Tim_Attard
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    Tim_Attard Active Member

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    [May 22, 2013]
    its deffinetely an aftermarket one as i bought it when i got the car and is loud, but the garage fitted it and said it tooka bit of modding to get it to fit so thats why im thinking it was 2.5 plus i measured it roughly and was closer 2.5
    #23
  25. superkarl
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    superkarl MAN OF STEEL

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    [May 22, 2013]
    looks to me like the catback reduces to stock size into that joiner which is on the cat pipe
    #24
  26. Tim_Attard
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    Tim_Attard Active Member

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    [May 22, 2013]
    so u reckon the aftermarket cat back is still 2.25? if thats the case should i get a bigger cat back or will it not matter to much?
    #25
  27. superkarl
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    superkarl MAN OF STEEL

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    [May 22, 2013]
    no. i think the catback is stock size at the end. purely so it fits the stock exhaust sleeve and mates up to the cat pipe.
    #26
  28. Tim_Attard
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    Tim_Attard Active Member

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    [May 22, 2013]
    hmm could well be, so if so i don't need anything as the decat would slot in to the joiner i have :) result

    thanks for the help guys takes me a while :)
    #27
  29. 16Klappe
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    16Klappe RacecaR forward is RacecaR backwards. Supporter

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    [May 22, 2013]
    Thanks Karl, I was losing the will to reply.

    Xxx
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