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Cat replacement pipe

Discussion in 'A3/S3 Forum (8L Chassis)' started by MOSSY, Sep 25, 2003.

  1. MOSSY
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    MOSSY Member

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    Does anyone know if any companys make a cat replacement pipe for the S3.

    I dont want a sport cat, just a replacement pipe.
    #1
  2. PaulRS3
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    PaulRS3 Active Member

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    funny you say that,

    an idea popped up about having a cat shaped pipe aka a milltek etc but with no catalyst honeycomb guts inside it.

    so it would for all intent and purposes look like a cat, but be a straight thru pipe inside /ubbthreads/images/graemlins/wink.gif ...

    stealth job! and look "normal" from outside

    but how sensitive are MOT cat tests? I assume your still have to put cat back come MOT?
    #2
  3. Ess_Three
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    Ess_Three Active Member

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    [ QUOTE ]
    but how sensitive are MOT cat tests? I assume your still have to put cat back come MOT?

    [/ QUOTE ]

    Very!
    There's not way you'll legitimately pass a current MOT emmissions test on a car as new as an S3, with no cat.

    And with regard to changing the cat each year...swapping it back in for the test...have you ever changed a cat?

    The whole exhaust has to be dropped...
    Getting the 6 mounting bolts undone where the cat meets the front pipe and bolts are heat soaked / corroded on is a nightmare...
    Getting the lamda sensor out when it's heat soak / corrosion siezed in is a nightmare...

    All in all, a real pain...and for what gain? The chance of a hefty fine if caught?
    What sort of gain do you think you'll see?

    The Milltek cats are all but see through and offer very little restriction in the way of flow, and they give very little power / torque gains...nowhere near what they claim in my testing....so the standard cat's can't be that bad. So why bother?

    Jusy my views...
    #3
  4. DaveCav
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    DaveCav Member

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    Just ordered a super sprint cat replacement pipe for mine
    #4
  5. PaulRS3
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    PaulRS3 Active Member

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    yes, i follow.

    just was something i had thought of. I dont intend on doing it.

    Infact, even having the improved driveability and smoother power delivery chat with Mr Milltek, i will still find it hard to shell out that sort of money unless my exhaust falls off.

    Intereting you say the milltek cat is all but see thru, the new one i saw wasnt. I was amazed anything would pass thru it.

    it "looked" restrictive, so the standard one must be even worse!
    #5
  6. Ess_Three
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    Ess_Three Active Member

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    [ QUOTE ]
    Infact, even having the improved driveability and smoother power delivery chat with Mr Milltek, i will still find it hard to shell out that sort of money unless my exhaust falls off.


    [/ QUOTE ]

    I have the full Milltek set up...worth the money? No.
    But, it is a nice piece of kit and gives the car a nice note...adds throttle response and top end pull...so a very worthwhile mod? Yes....just a bit expensive in my view.


    [ QUOTE ]

    Intereting you say the milltek cat is all but see thru, the new one i saw wasnt. I was amazed anything would pass thru it.
    it "looked" restrictive, so the standard one must be even worse!

    [/ QUOTE ]

    Hmm..I can see through mine...you can't see through like an open pipe but you can see objects through the cat material...this is with 100 cell cats.

    I also have a VR6 Corrado Milltek cat sat here...you can see through that too!

    Compared to the standard effort which lets no light through at all...it's amazing it works at all...but it does!


    Personally, I think de-catting adds next to nothing in power...perhaps a few BHP but you can get that with the Milltek cats...sure it's cheaper, but over a few years of changing back for the MOT, is it worth it?..A few 'swap it in, MOT it, then swap it out' carry on's will soon have the cost adding up - assuming you have to use a garage to do it.

    ..and if you get caught? Serves you right... /ubbthreads/images/graemlins/tongue.gif
    #6
  7. Gambba
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    Gambba Active Member

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    As suggested by my exhaust specialist is just to cut the CAT out and put mounting flanges on either end do the same on a straight through pipe and then mounting flanges on the main exhaust pipes. I would of thought the same is possible for the S3 even with the twin CAT setup and at 225 Euros that I was quoted for my A3T it's a bargain....and you can easily swap it in and out, as long as you clean the bolts and nuts occasionally.
    #7
  8. MOSSY
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    MOSSY Member

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    Gambba

    Yes your right it is dead easy to change, as long as you give the bolts a soaking in WD40 first.

    As for the MOT, i know of a few garages that will put the CAT back on for you for the MOT and then take it off again afterwards. They may make a note on the receipt to say what they have done to over there backs, But remember they dont write it on the MOT they write in on a receipt which you can throw away.

    How many people here have been pulled over by the plod and had there emisions checked? not bloody many.
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  9. MOSSY
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    MOSSY Member

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    Just a carry on from above post.

    With regards to there being hardly any difference in performance when having the CAT on and it being off, I know its not the same car but when I had my EVO and did the same, there was a hell of a difference and you could feel it. All cars with cats on are restricted.

    I know what i would buy.
    #9
  10. RichA3Turbo
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    RichA3Turbo ...Watching you! Staff Member Moderator

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    [ QUOTE ]
    MOSSY said:
    it. All cars with cats on are restricted.


    [/ QUOTE ]

    Yeah your right, all cars with cats on ARE restricted... to a certain extent anyway! You cant compare 2 completely different cars on power, it just doesnt work!

    Now, i reckon that u would see a bigger gain by putting sports cats on the A3 than you would the S3, due to the A3's single cat (which when chipped isnt much less power than a 210 S3, sometimes more) and the S3 having twin cats.

    Rich
    #10
  11. Stuart_A3_Turbo
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    Stuart_A3_Turbo Member

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    ive got a decat on my A3T and it made a great difference. Ive got a powerflow exhaust too, so the bloke put mounting flanges, as mentioned above, so its just a case of removing the decat pipe and slotting in the cat. He also said that he would swap it free of charge as he will do the annual check on my powerflow at the same time. It gets checked yearly for the guarantee purposes. So, for something that will take all of 10 mins to swap back its well worth it and combined with a stainless steel exhaust system, does give good gains.
    #11
  12. Ess_Three
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    Ess_Three Active Member

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    [ QUOTE ]
    ive got a decat on my A3T and it made a great difference.


    [/ QUOTE ]

    And what precisely is a great gain?
    A seat of the pants gain on your calibrated rear end?...or a quantifiable dyno proven gain?

    I for one would love to see proof that cat swaps / removals make 'great' gains of VAG cars...on many of the Japanese stuff...yes...but not on the VAG stuff...unless you have the dyno graphs to show otherwise.


    [ QUOTE ]

    So, for something that will take all of 10 mins to swap back its well worth it and combined with a stainless steel exhaust system, does give good gains.


    [/ QUOTE ]

    Ahh..10 mins on a 4 poster ramp with an exhaust fitter doing the swap...how long on your garage floor with you doing the work?

    I've still to see proof - before and after plots, same operator, same rollers etc - that cat removals make 'good' gains...

    Exhaust systems dont. That's dyno proven. Not 'great' or even 'good' power gains...some gain, yes...but certainly not enough to qualify for what I'd describe as 'great' or even 'good'.

    Of course, it is possible that FWD 1.8Ts behave completely differently to all other VAG cars...but other VAG vehicles with similar exhaust lay-outs and power outputs to an A3 certainly don't benefit hugely from removing the cat.

    Unless...as I've said, you can quantify and prove the gains.

    I'm not out to have a go here...but expressions like 'great' and 'good' are interpreted differently by different people...and I just don't believe that the gains are that good.

    #12
  13. JayBeeS3
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    JayBeeS3 Member

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    does anybody know where the lambda sensor is in the exhaust of an S3 (oktober 2000 model). According to the Exhaust specialist (talked to them over the phone) it can be either:
    - before the cat (thats good)
    - or in the cat (bad)
    - or after the cat (good again)
    The position of the sensor determines wether the car has to be blueprinted after the cat has been replaced.
    (and that makes a difference in the price of the de-catting.
    Thanks in advance!!
    /ubbthreads/images/graemlins/beerchug.gif
    #13
  14. MOSSY
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    MOSSY Member

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    I think we should wait and see what Davecav comemnts are when he gets his fitted.

    Dave

    How much have you paid for the de-cat, if you dont mind me asking.


    #14
  15. Ess_Three
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    Ess_Three Active Member

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    [ QUOTE ]
    Glen,
    Based on GolfTTish's mods to obtain 250hp one of which was a new exhaust system and so had proven that an exhaust change would give a nice increase. Whether the increase is down to a restrictive downpipe mainly, as has been suggested, or a combination of the CAT and downpipe is another thing. When speaking to the guys here at EPS they are under no doubt that the most restrictive part in the A3 system is the CAT and said that actually the backboxes from VAG are very free flow.


    [/ QUOTE ]

    There is no doubt that the downpipe is ****.
    An upgrade here is well worth the money...

    With regard to the cat...my previous comments stand:
    Prove to me that a 'great' or even a 'good' gain is achievable by removing the cat...I've certainly never seen proof of huge gains.

    ..if Milltek sports cats - which are see through and hence offer virtually nil restriction - only give about 1-2 BHP I just can't see where the extra is coming from to constitute a 'good' power gain.

    Or maybe some people class 1-2 BHP as a good, or heaven forbid, a great gain...I certainly dont. 10BHP at the wheels to me, is a good gain. 20, a great gain.

    Added to the risk of getting hammered by plod for emmissions (and yes I've been tested at the roadside twice in the last few years) and the hassle of changing the pipe / cat prior to MOT - certainly not a 10 minute job as I've just done a similar thing today - makes the whole cat bypass thing a bit of a damp squib in my book.
    But each to their own.
    #15
  16. Ess_Three
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    Ess_Three Active Member

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    [ QUOTE ]
    I see it appears to be both one before and after the CAT, but I'm sure something could be done to sort that out...

    [/ QUOTE ]

    There is...
    Keep the catalyst!! /ubbthreads/images/graemlins/smirk.gif

    Even with Milltek high flow cats you can get problems with DTCs if you are running very high boost and making decent power.
    I get the occasional 'Catalyst Efficiency Below Threshold' DTC...which gives no problems at all except logging in the ECU...no engine check light or soft limp mode.

    So, maybe you can run without a cat and the ECU not bother, despite the faults being logged....unless there is a second trigger for a later stage of warning that initiates limp mode. Unfortunately I can't help with that...
    #16
  17. Gambba
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    Gambba Active Member

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  18. DaveCav
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    DaveCav Member

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    [ QUOTE ]
    Ess_Three said:
    [ QUOTE ]
    Glen,
    Based on GolfTTish's mods to obtain 250hp one of which was a new exhaust system and so had proven that an exhaust change would give a nice increase. Whether the increase is down to a restrictive downpipe mainly, as has been suggested, or a combination of the CAT and downpipe is another thing. When speaking to the guys here at EPS they are under no doubt that the most restrictive part in the A3 system is the CAT and said that actually the backboxes from VAG are very free flow.


    [/ QUOTE ]

    There is no doubt that the downpipe is ****.
    An upgrade here is well worth the money...

    With regard to the cat...my previous comments stand:
    Prove to me that a 'great' or even a 'good' gain is achievable by removing the cat...I've certainly never seen proof of huge gains.

    ..if Milltek sports cats - which are see through and hence offer virtually nil restriction - only give about 1-2 BHP I just can't see where the extra is coming from to constitute a 'good' power gain.

    Or maybe some people class 1-2 BHP as a good, or heaven forbid, a great gain...I certainly dont. 10BHP at the wheels to me, is a good gain. 20, a great gain.

    Added to the risk of getting hammered by plod for emmissions (and yes I've been tested at the roadside twice in the last few years) and the hassle of changing the pipe / cat prior to MOT - certainly not a 10 minute job as I've just done a similar thing today - makes the whole cat bypass thing a bit of a damp squib in my book.
    But each to their own.

    [/ QUOTE ]

    It takes 10-15 mins max to swap your cat round did it on friday
    #18
  19. Gambba
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    Gambba Active Member

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    [ QUOTE ]
    Ess_Three said:
    There is no doubt that the downpipe is ****.
    An upgrade here is well worth the money...

    With regard to the cat...my previous comments stand:
    Prove to me that a 'great' or even a 'good' gain is achievable by removing the cat...I've certainly never seen proof of huge gains.

    ..if Milltek sports cats - which are see through and hence offer virtually nil restriction - only give about 1-2 BHP I just can't see where the extra is coming from to constitute a 'good' power gain.

    Or maybe some people class 1-2 BHP as a good, or heaven forbid, a great gain...I certainly dont. 10BHP at the wheels to me, is a good gain. 20, a great gain.

    Added to the risk of getting hammered by plod for emmissions (and yes I've been tested at the roadside twice in the last few years) and the hassle of changing the pipe / cat prior to MOT - certainly not a 10 minute job as I've just done a similar thing today - makes the whole cat bypass thing a bit of a damp squib in my book.
    But each to their own.

    [/ QUOTE ]

    I think like yourself, I would be interested to see some before and after RR results based on the removal of the CAT.
    #19
  20. simont
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    simont Member

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    yes it will be interesting to see any before/after RR results concerning a cat bypass on an S3/TT.

    I looked into doing this early this year and AMD's advice was that the standard S3/TT cats are relatively free flowing and don't really restrict things unlike the downpipes as Glen has suggested.

    #20
  21. Ess_Three
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    Ess_Three Active Member

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    [ QUOTE ]
    DaveCav said:

    It takes 10-15 mins max to swap your cat round did it on friday

    [/ QUOTE ]

    You are obviously a better worker than me.

    It took me and a qualified VW tech a good couple of hours to swap mine at the local dealer....since the North of Scotland weather is not good for preventing corrosion we had the following problems:

    Lamda sensor seized in place.

    Cat to downpipe bolts seized.

    Cat to exhaust sleeved joint seized in place.

    All exhaust bolts required to be removed to get the cats out / new ones in...all corroded and tight.

    The only thing that came off easily was the cat heat shield!


    This was done in the local dealership, on a 4 post ramp, with a qualified VW tech, all the correct tools and the use of oxy-ecetylene!


    you were lucky...
    Obviously I was unlucky...

    But the comment stands, for anyone not as fortunate as yourself, the job can be a right bitch.
    And I still havent seen proof of any gains...
    #21
  22. DaveCav
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    DaveCav Member

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    m8 if id have done it myself i would have been there all week !! Had it done at zorst place in Bradford , Bolts were a bit stiff but soon had them off , Only 2 guys , Heat shield didnt need to come off??

    How old is your s3 m8?
    #22
  23. DaveCav
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    DaveCav Member

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    Had a middle section fit yesterday from back box to cat replacement sounds a fair bit beeter now , Needs looking at tho as it clanks about abit ! feels alot more free reving now if that makes sense lol £70 it was
    #23

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