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What size bore for stainless exhaust system??

Discussion in 'Audi S4/A4/A4 Cab (B7 Chassis)' started by Stu.Audi, Mar 26, 2014.

  1. Stu.Audi
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    Stu.Audi Member

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    [Mar 26, 2014]
    Am looking get a catback system so garage said 2" bore but was wonder if can run on 2.5" bore for 2.0 tdi???
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  3. jjmurphy21187
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    jjmurphy21187 Tiptronic

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    [Mar 26, 2014]
    Less back pressure will allow for better air flow, so larger is usually better. Will you notice a difference from 2" to 2.5"... I wouldn't like to say. Physically you should be able to fit any bore you like, it's more a question of if there will be any benefit.

    One thing to bear in mind is the size of the existing flanges and pipes... if you leave your downpipe etc as a 2" and everything back from the CAT as 2.5", you still have the bottle-neck of the front section in the system.

    Is the car remapped, does it have a standard or upgraded turbo?
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  4. Stu.Audi
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    Stu.Audi Member

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    [Mar 26, 2014]
    Cheers
    Car total.standard
    As want it all done.before remap it
    Turbo r.standard is it there a upgraded turbo!! As am New lol
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  5. jjmurphy21187
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    jjmurphy21187 Tiptronic

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    [Mar 26, 2014]
    Not sure on the turbo front for the 2.0tdi... there is an upgrade for petrol engines (K03, K04), but I'm not sure the same exists for the tdi.

    One member has fitted the 3.0tdi turbo innards into the 2.7tdi turbo, however I believe this was a custom job.

    If it's being remapped, 2.5" will provide less resistance to the turbo and should allow easier breathing for the engine. 2.5" will no doubt be more costly than 2" due to the extra material required. Given the slight difference in performance gains on a 2.0tdi, (you would need to wait for someone with the same engine to chip in here) depending on the additional cost you may not be able to justify 2.5" over a 2" pipe...
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  6. lynallbel
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    lynallbel Active Member

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    [Mar 26, 2014]
    Must be bigger than 2 inch as std surely?
    I would hazard a guess at least 2.5 inch, forget capacity think bhp
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  7. Stu.Audi
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    Stu.Audi Member

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    [Mar 26, 2014]
    Ok need to find out what size standard tho
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  8. DieselJake
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    DieselJake God Mode

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    [Mar 26, 2014]
    2.5's about right for most applications, there's actual calculations which can be done to get it exact but generally people just do same as the masses. Bigger exhausts benefit turbo cars (like yours :icon_thumright:) better, just need a comfortable medium of sound and optimum performance.

    one of these would grab some attention though haha

    [​IMG]
    Last edited: Mar 26, 2014
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  9. jjmurphy21187
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    jjmurphy21187 Tiptronic

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    [Mar 27, 2014]
    Just go for 2.5" then you won't be left wondering 'what if' for that little extra performance. I'd recommend getting the DPF gutted/removed whilst you're there too... MOT is a grey area but mine past after the new regs came in and I've had it replaced with a silencer.

    If you were looking for all-out performance you'd probably want mandrel bends too... but these cost more and will probably not be necessary unless you're a perfectionist like me :whistle2:
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  10. Stu.Audi
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    Stu.Audi Member

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    [Mar 27, 2014]
    Yeah was thinking dpf removed egr delete and remap after this plus timer belt
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  11. Gazwould
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    Gazwould Active Member

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    [Mar 27, 2014]
    I would think the std system is 2.25" .
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  12. Stu.Audi
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    Stu.Audi Member

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    [Mar 28, 2014]
    That wot I thinking defo be 2.5 then
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