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DeCat pipe arrived!

Discussion in 'A3/S3 Forum (8L Chassis)' started by Dave_Bayern, Jul 9, 2007.

  1. Dave_Bayern
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    Dave_Bayern Slipping at 3.5Krpm

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    [Jul 9, 2007]
    £100 from eBay, thought for the price I might as well try it....

    After having investigated the current work I am doing to the car, and the Bhp I want to achieve, a new downpipe was needed, and a high flow cat.

    However, sports cats are stupid money, and I won't be needing to go through emissions tests on this car so I thought I'd just de-cat.

    Initial findings are its VERY nicely welded, good solid pipe, 3" Bore, leading to 2.5" and 2" at the end of the decat pipe.

    My current Milltek is 2.5" I think so I'll end up cutting off the 2" section and joining to another pipe.

    Anyway, pics here, looks pretty decent, I'll do a test fitment tonight.....

    [​IMG]

    [​IMG]

    [​IMG]
    #1
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  3. sitrials
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    sitrials Member

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    [Jul 9, 2007]
    £100 really??? deffinately for the K04 or is this for a different turbo?!?
    Si
    #2
  4. Dave_Bayern
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    Dave_Bayern Slipping at 3.5Krpm

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    [Jul 9, 2007]
    K03 and K03s....

    THS Parts on eBay
    #3
  5. sitrials
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    sitrials Member

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    [Jul 9, 2007]
    ahh i see
    very good buy indeed!
    #4
  6. golf
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    golf ***** rent boy VCDS Map User

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    [Jul 9, 2007]
    I've always been interested in this part, let us know the difference it makes. I hear these things make the turbo spool up quicker and increase noise.
    #5
  7. Dave_Bayern
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    Dave_Bayern Slipping at 3.5Krpm

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    [Jul 9, 2007]
    I'll be mighty annoyed if it increases noise. The idea is for it to speed up turbo spooling and allow better flow through the system, thus maintaining peak pressure.
    #6
  8. simch
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    simch Active Member

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    [Jul 9, 2007]
    I reckon it will be noisy as a noisy thing at a noise convention!

    The miltek system is reknowened for being boomy on a3s and golfs even with the sports cat in place...
    #7
  9. Dave_Bayern
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    Dave_Bayern Slipping at 3.5Krpm

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    [Jul 9, 2007]
    Yeah, tell me about it. Proper hanging of the milltek makes a HUGE difference though, as mine went from boomy and unbearable at motorway cruising to being perfectly silent except when I put my foot down.

    I don't mind too much as long as its not above 98Db so I can conform to track noise limits.
    #8
  10. Jampublic
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    Jampublic Taking it easy..

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    [Jul 9, 2007]
    Looks nice Dave, need any help? ;)
    #9
  11. Tallpaul
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    Tallpaul Member

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    [Jul 9, 2007]
    The turbo still requires a degree of back pressure. The exhaust can actually be too free flowing. IIRC the reduced back pressure affects the sealing and leads to poor lubrication and premature turbo death.

    Also does your car have a wide-band lambda? Two problems here, one you'll get a CEL light and two, how will the ECU monitor the AF ratio post ignition?

    What map are you running?

    Do you have VAG-COM to monitor the effets of removing the CAT?
    #10
  12. Dave_Bayern
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    Dave_Bayern Slipping at 3.5Krpm

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    [Jul 9, 2007]
    The back pressure should be provided by the midsection silencer and back box, so it should be OK there, as you can see the decat pipe also reduces in size, so this will cause a slight constriction in flow, providing some pressure. There are plenty people running decats on Mk4's so I can't imagine it being a massive issue with the turbo.

    I have an AGU so only a pre-cat Lambda, so I'll get no error lights.

    You can have the remapping agents take out the second lambda sensor (as in, stop monitoring) if you have a later car too.

    I currently have a superchips map, but once the FMIC is fitted, it's going Custom Code.

    I have VAG-COM, but there wont be anything to monitor, as its an AGU and thus doesnt measure the post cat ratio.
    #11
  13. Tallpaul
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    Tallpaul Member

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    [Jul 9, 2007]
    The definition of premature failure is gonna depend on the amount of miles you do. If you only do 6k/year then you may never get the turbo to the point of failure. It's something worth considering if your blower is already high mileage or you plan to clock a lot of miles on it.

    Not having any way of logging EGT's or A:F isn't advisable for going the route of tuning you have chosen. Even running slightly lean is bad, especially as it sounds like you are going to be using this a track car (i assume that's why it won't need an MOT)?

    Are Custom-Code able to map the ECU in AGU? Not saying they aren't, just a lot of tuners won't touch it because it can't be flashed via the OBD port.
    #12
  14. Dave_Bayern
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    Dave_Bayern Slipping at 3.5Krpm

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    [Jul 9, 2007]
    I can't see why it would fail? It'll spool quicker with the larger downpipe and work harder due to the extra boost a remap will push through it, but it's never going to produce massive reductions in usable life unless as you say, you're doing 30K a year in the car.

    The Turbo is a K03s with 31K on it, and it is immaculate, certainly comapred to my K03, which was covered in white deposits (so it was possibly running lean), and that was ultra reliable, never serviced, 130K miles.

    Again, why would I need to log the A:F ratio, bearing in mind the car will be remapped against a set A:F ratio from the word go? I can understand if you change things, such as add a decat afterwards...

    Yeah, Custom code will remap the AGU, although they need the ECU posted to them, they remap it with their chosen map, gets sent back to CC dealer, who then stick the car on the rollers and fine tune the map.

    They say 240Bhp and 250ft.lbs, hence the need for the larger downpipe and FMIC.
    #13
  15. mwstewart
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    mwstewart Member

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    [Jul 9, 2007]
    The cat is the most effective silencer in the system (along with the Turbo itself), so you will notice an incrase in noise Dve.
    #14
  16. Tallpaul
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    Tallpaul Member

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    [Jul 9, 2007]
    Fair enough, if you are satisfied.

    Just cautionary notes as you are going beyond the normal chip and exhaust tune that the majority take their cars too.

    If i come across the article i read on why a turbo needs a certain amount of back pressure then i'll post it up.

    240bhp/250lb_ft sounds a realistic estimate if the FMIC keeps charge temps low enough. I'd still be wary of fueling though, it's always better to run rich (especially as you won't have a CAT to damage ;)).

    Oh, and it's gonna be LOUD.
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  17. Dave_Bayern
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    Dave_Bayern Slipping at 3.5Krpm

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    [Jul 9, 2007]
    That turbo article would be cool!

    I still have the middle silencer so it should be better than none, but yeah, it will be loud, as long as its not 'too loud' for tracks I'll be happy.

    Its already loud and I have the silenced Milltek!
    #16
  18. Kivi
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    Kivi New Member

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    [Jul 9, 2007]
    IMO in turbocharged cars the easier the flow of the exhaust gases the better. Check out what it's like in powerful 1/4 mile cars - they often have the exhaust ending just behind the front wheels.
    However backpressure is desired in the N/A cars - that's for sure.
    #17
  19. KEF A3 20V T
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    KEF A3 20V T Turbo's Rule

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    [Jul 9, 2007]
    A decrease in back pressure lets the turbo spool up faster but it also makes the turbo spin faster at full revs creating slightly more boost. BUT everything has a limit to how fast it will spin before it gives up.

    lots of people use decats and they are fine, just trying to enlighten u as to what added stresses you are adding.

    Kivi:
    quater mile cars are built for optimal performance not day to day drivers so they dont really care about turbo life as the engine running hours will be so short.

    just my 2p
    #18
  20. Kivi
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    Kivi New Member

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    [Jul 9, 2007]
    Yes, you're right. But consider the fact that normally you have the car's ECU controlling the boost pressure through wastegate - protecting turbocharger against overspinning.

    I have a complete 2,5" custom exhast with a decat and and a 3" downpipe in my S3 and I haven't noticed a significant boost gain - something around 0,1 throughout the whole range of revs.
    Although the car is noticeably quicker in the high revs and pulls strongly until the red line - that was the main performance gain after having the exhaust made. The peak boost comes a bit quicker as well.
    #19

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