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    Thread: Milltek Cat Bypass pipes (TTRS)

    1. Member
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      05-02-2012 01:18 AM #1
      Hi all,


      Really been happy with my APR products so far on my GTI. All their stuff works seamlessly and I cant recommend them enough. Alas, I went a bit over my budget ordering the TTRS and I started thinking about small mods to do gradually myself rather than going all in for an APR Stage 2.

      What sealed this for me was the new memo going out in North America about Audi attempting to blanket void peoples warranties if mods are found. You never know out of the box if your new car will be a lemon or have some teething issues, best not to give them any excuse to deny claims....

      This lead me to looking at the Milltek Cat Bypass pipes since its a very easy bolt on and buying the muffler section of the OEM Sport Exhaust. Since the O2 sensor is on the primary cats, there should be no issues....( or a quick swap back stock before heading into the stealership )


      I was hoping to hear from any/ all of you who have gone this route. Specifically the difference in sound and feel from stock to cat bypass.

      I really love the Sport Exhaust sound and I have yet to hear an aftermarket one that sounded better. Disclaimer being I've only ever compared HD videos.

      I know MitchyRS has been running crazy numbers with just a racing filter in the stock airbox, bypass pipes and chipping.

      I thinking a HPA motor mount might also help the shifter issues and the Six Sigma shifter should be available soon.


      I think I may have a muffler lined up so it will be a straight swap out of my stock OEM muffler instead of $1500 if Audi had their way
      Last edited by YYC Dubber; 05-02-2012 at 01:57 AM.
      2007 GTi Black Magic, APR Stage 2+
      2012 TTRS Sepang Blue on Titanium Blades.....

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      05-02-2012 05:01 AM #2
      You've seen myself and Domm post many times about this. We both love the setup. It's super cheap and it sounds great. Coming from the non-sport exhaust, you're going to love it. It's got a nice grumble and bark to it. It does drone a little at 2k, but it's not terrible and you can easily shift out of it. Everyone likes the way my car sounds.

      My only complaint about it is the flapper. It's never open when *I* want it to be. Even in sport mode, it closes back up. It only opens under 3k RPM in 1st, 4th and 6th gears. It stays closed (under 3k) in 2nd, 3rd and 5th. I don't know why. I want it open under 3k in 1st, 2nd and 3rd. It can close up in 4th (again, under 3k only) and higher because those are cruising gears with drone anyway. But when you're hauling ass over 3k in any gear, it sounds great. It's loud enough without warranting an arrest.

      If I were to do this all again, I would stick with the base exhaust and just get the APR RSC instead. Simply because it doesn't use a flapper and it always sounds angry, which I like.

      - Jeremy -

    3. 05-02-2012 08:00 AM #3
      hmm are you sure, i think mine opened above 3k in any gear...

    4. Member LongviewTx's Avatar
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      05-02-2012 08:11 AM #4
      Quote Originally Posted by YYC Dubber View Post

      ... the new memo going out in North America about Audi attempting to blanket void peoples warranties if mods are found.
      Is there a thread discussing this further. I missed it.
      2012 Audi TTRS Coupe, Sepang Blue, Ti Pack/Sport Exhaust w/ Leather/Alcantara

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    5. Junior Member turbojlo's Avatar
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      05-02-2012 08:45 AM #5
      YYC Dubber get the bypass pipes. With the stock exhaust or even better stock sport exhaust they sound awesome!

      Some good feedback here from someone who drove behind me and also drove my TT RS:
      http://forums.quattroworld.com/tt2/msgs/19180.phtml

      There is also a video in that thread, but there is a lot of wind noise.

      Another video here but only the first 30 seconds are worth watching and even then they don't give you the full impression of the sport exhaust + cat bypass:
      http://www.youtube.com/watch?v=ubWeIbhdJ4I

      I'm going to be installing a catless downpipe and replacing my Milltek cat bypasses with midpipes with high flow cats. So if anyone wants the Millteks with ~1000 miles on them for $250 let me know.

      Jeremy have you considered putting a zip tie on the vacuum line that controls the exhaust flap so that the flap is always open in ALL RPMs and is not tied to the Sport button?

      Otherwise your only other option is to have a tuner like EPL change the code in your ECU to have the sport button open the flap at all RPMS when on, wouldn't hurt to get the engine tuned to 400+hp at the same time too
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      05-02-2012 10:45 AM #6
      Quote Originally Posted by tdi-bart View Post
      hmm are you sure, i think mine opened above 3k in any gear...
      Yeah, it does. I'll try to make a little table the illustrate how the flapper works.



      You can see at the flapper will open above 3k in any gear and in any mode. But it stays closed under 3k *EVEN IN SPORT MODE* in some gears but not in others. I don't know why.

      - Jeremy -

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      05-02-2012 10:47 AM #7
      Quote Originally Posted by turbojlo View Post
      Jeremy have you considered putting a zip tie on the vacuum line that controls the exhaust flap so that the flap is always open in ALL RPMs and is not tied to the Sport button?

      Otherwise your only other option is to have a tuner like EPL change the code in your ECU to have the sport button open the flap at all RPMS when on, wouldn't hurt to get the engine tuned to 400+hp at the same time too
      Yeah, I did the flapper mod when I put in the Milltek pipes. It sounds awesome, but the drone at 2k was just a bit much. Actually, it didn't really bother me. It just made the body panels at the rear of the car rattle, which I really hate. So I reconnected it after a few weeks.

      - Jeremy -

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      05-02-2012 11:32 AM #8
      Quote Originally Posted by - Jeremy - View Post
      Yeah, it does. I'll try to make a little table the illustrate how the flapper works.



      You can see at the flapper will open above 3k in any gear and in any mode. But it stays closed under 3k *EVEN IN SPORT MODE* in some gears but not in others. I don't know why.

      - Jeremy -
      Where did you get this chart? If you made it just from how your own car behaves, then it may not be representative of how everyone's car behaves (e.g., if your car's flapper is acting up in some way).

      My car's flapper sounds like it opens below 3k RPM during 1st-2nd shifts, and the closes back up again a second later. It's very odd.
      2012 TT-RS in Suzuka Gray

    9. 05-02-2012 11:44 AM #9
      Milltek Bypass pipes & Flapper mod = Heaven.
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    10. Junior Member turbojlo's Avatar
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      05-02-2012 01:19 PM #10
      Quote Originally Posted by - Jeremy - View Post
      It just made the body panels at the rear of the car rattle, which I really hate. So I reconnected it after a few weeks.
      Strange! Mine doesn't do that, but mine is also a 2012 with only 1500 miles. I assume yours is older/has more miles?
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      05-02-2012 02:23 PM #11
      Quote Originally Posted by Marty View Post
      Where did you get this chart? If you made it just from how your own car behaves, then it may not be representative of how everyone's car behaves (e.g., if your car's flapper is acting up in some way).

      My car's flapper sounds like it opens below 3k RPM during 1st-2nd shifts, and the closes back up again a second later. It's very odd.
      I made it based on what my car does. Mine behaves just like you're describing. Once the car realizes that it's in second gear, it closes the flapper back up. Exactly the same as yours. I would be surprised if anyone else says their car behaves differently.

      - Jeremy -

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      05-02-2012 02:26 PM #12
      Quote Originally Posted by turbojlo View Post
      Strange! Mine doesn't do that, but mine is also a 2012 with only 1500 miles. I assume yours is older/has more miles?
      Mine's a 2012 and only had 1000 miles on it when I did the flapper mod. The vibration wasn't significant but it was enough to annoy me. I'm really sensitive to rattles and buzzes that aren't supposed to be happening in a new car. A Lotus, I can understand. But it bothered me so I reattached the flapper.

      - Jeremy -

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      05-02-2012 03:03 PM #13


      Love it.
      Last edited by DrDomm; 05-02-2012 at 03:32 PM.
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    14. 05-02-2012 04:19 PM #14
      i can hear the flap open after idle warms up and the revs drop, however, to me it seems the flap opens even more with sport on above 3k, because as soon as you hit 3k it goes even louder with the sport mode already on... anyone else confirm this?

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      05-02-2012 04:42 PM #15
      Hoping the boys like BB can chime in on the AWE system, specifically how it operates the flapper. I know Jason ( imodR) had a Scorpion exhaust uses a motor to operate the flapper so I was thinking about retrofitting this to on the cat pass/OEM muffler system you all have.

      I assume Audi went with the vacuum type system for simplicity and cost effectiveness, but I don't like that it seems to have a mind of its own.
      2007 GTi Black Magic, APR Stage 2+
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      05-02-2012 05:17 PM #16
      Quote Originally Posted by tdi-bart View Post
      i can hear the flap open after idle warms up and the revs drop, however, to me it seems the flap opens even more with sport on above 3k, because as soon as you hit 3k it goes even louder with the sport mode already on... anyone else confirm this?
      Yeah, it depends on what gear you're in. 1st, 4th and 6th don't do this, but 2nd, 3rd and 5th do. At least on my car, anyway...

      - Jeremy -

    17. Junior Member DaveTT's Avatar
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      05-02-2012 06:31 PM #17
      I have the oem sports exhaust, was originally going to get the AWE switch path system but decided to try the Milltek Bypass pipe 1st. I also unplugged the vacuum hose on the flapper so its always open. For me, this is the perfect setup right now. Car sounds great and it I can convert back to stock at anytime. And did I mention I love the sound

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      05-02-2012 08:57 PM #18
      http://www.youtube.com/watch?v=RatrT...e_gdata_player

      my mistake, not a scorpion exhaust but a miestershaft exhaust.
      has anyone looked at adding components or beefing up the vacuum system so that it the valve only opens and closes when u press the button?

      I am willing to take it to a fabricator so see what they could do... Perhaps a an extra diaphragm chamber to keep up vacuum in situations the stock system momentarily doesn't provide enough and this the flap closes...
      Last edited by YYC Dubber; 05-02-2012 at 09:12 PM.
      2007 GTi Black Magic, APR Stage 2+
      2012 TTRS Sepang Blue on Titanium Blades.....

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      05-02-2012 09:07 PM #19
      Quote Originally Posted by Marty View Post
      Where did you get this chart? If you made it just from how your own car behaves, then it may not be representative of how everyone's car behaves (e.g., if your car's flapper is acting up in some way).

      My car's flapper sounds like it opens below 3k RPM during 1st-2nd shifts, and the closes back up again a second later. It's very odd.
      it's odd because I think the system is not very well designed. They went with a vacuum system for simplicity in comparison to a motorized system but I don't think the system can cope with large changes in vacuum properly thus the Sport button does not have full authority over the flapper.

      if someone has the maintence technical manual or a link to where I can download it, I will look over the schematic and see if I can understand it. I have some background in vacuum driven systems and instruments that are used in aviation, and I have a few thirsty AME buddies I could pay in beer....
      Last edited by YYC Dubber; 05-02-2012 at 09:18 PM.
      2007 GTi Black Magic, APR Stage 2+
      2012 TTRS Sepang Blue on Titanium Blades.....

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      05-02-2012 09:41 PM #20
      here's the Audi warranty issue thread:
      http://forums.vwvortex.com/showthrea...-warranty-flag
      2007 GTi Black Magic, APR Stage 2+
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      05-03-2012 12:59 AM #21
      Forge Motorsports has the Scorpion decat pipes for much cheaper, and are pretty much identical (a 4" pipe is a 4" pipe).

      Jeremy and Domm have covered it. Great mod, cheap, and easy to install.
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