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  1. #1
    Senior Member Two Rings
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    Exhaust setup for 1.8t

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    I tried looking up diagrams for the stock exhaust on an 01 1.8t but I can't seem to find any links work, does anybody have a valid link for a diagram for the stock exhaust on a 1.8t b5, even just if somebody could explain the individual piping and parts that come after the cat. Reason being I'm planning on straight piping my car but I don't want to do it all the way from the cat back and I need to know where everything else on my exhaust is and what it's called so I can determine where I want to start the straight pipe. As you can see I'm pretty new to this so please bare with me, I still have a lot to learn..

    And I'm planning on going with 2.75" piping, does that sound about right?
    Last edited by Clewe; 01-01-2011 at 03:16 PM.

  2. #2
    Active Member Two Rings
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  3. #3
    Senior Member Two Rings
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    Yeah that does help and I can kind of follow along on what he's saying, but I don't even know what is all on an exhaust and what parts are where, and what they are called. So before I even look into that, I kind of need a diagram or even some explanation on where everything sits on an exhaust and what the parts are called starting from the cat and going back. Otherwise I can't really follow along with these write ups because I don't even know the names of the piping and where they are. Sorry for any inconvenience I feel like kind of a tool coming on here and wasting your guys times with something that is so simple to you guys, but I'm trying to learn and this seems like the best way to do it, anyways thanks again in advanced.

  4. #4
    Veteran Member Four Rings seanj130's Avatar
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    If i recall from when i straight-piped my car.. The Exhaust i believe is 2.25, 2.75 should be good on your car. Straight-piping your car is very loud and you will be getting tickets monthly.

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  5. #5
    Veteran Member Four Rings
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    Quote Originally Posted by b6nukka View Post
    avoid this thread like the plague. The OP has decided it better to let the nuthuggers that work for the exhaust companies tell those of us with engineering backgrounds how gas flow really works. This thread is a great starter for someone with a 4.2 V8 with no mods, and not a clue how physics work. After the OP belittled a few of us because we disagreed with what he said I had enough of it. There is absolutely no similarities between the 1.8t and the 4.2, so don't go to that topic if you really want to know anything about exhaust.

  6. #6
    Senior Member Two Rings
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    Haha thanks for all the responses guys, but is there anyway i could just get an exhaust diagram or how its setup after the cat. Thanks in advanced.

  7. #7
    Veteran Member Four Rings turbo kraut's Avatar
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    you have your turbo, the the cat, then the downpipe, flexpipe, exhaust to resonator, exhaust to muffler.... if you want to get better exhaust you can go with a hfc, then a better downpipe.... straight exhaust to a hf resonator to exhaust to something like a magnaflow 14815(or any other highflow muffler)



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  8. #8
    Veteran Member Four Rings $teady$upreme's Avatar
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    To be honest, if you don't plan to go bigger turbo in the future, 2.75" ID is too big for your k03. Maybe try 2.5" with k03~
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  9. #9
    Veteran Member Four Rings geeky's Avatar
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    Quote Originally Posted by $teady$upreme View Post
    To be honest, if you don't plan to go bigger turbo in the future, 2.75" ID is too big for your k03. Maybe try 2.5" with k03~
    I was running a 2.5" with a K04 PC16 setup and my buddy running an APR Stage3 kit is also running a 2.5", but both exhausts are 2.5" straight off gutted cats/test pipes.

    heres what mine sounded like, the exhaust setup is listed in the video info.

    http://www.youtube.com/watch?v=QqQEBQwMgSM

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  10. #10
    Senior Member Two Rings
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    Quote Originally Posted by $teady$upreme View Post
    To be honest, if you don't plan to go bigger turbo in the future, 2.75" ID is too big for your k03. Maybe try 2.5" with k03~
    Thanks for letting me know. And why do you think it would be better to not go any bigger than 2.5

  11. #11
    Veteran Member Four Rings geeky's Avatar
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    I recall reading that going too big on an exhaust has the same effects as going too small. When the exhaust gases leave the car, they pulse and create a resonance within the exhaust. When the exhaust becomes too big, it alters the resonance and in turn creates turbulence within the piping, creating chaos within the back pressure, just as if the exhaust was too small to let the gases properly free-flow.

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  12. #12
    Veteran Member Four Rings turbo kraut's Avatar
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    too small = too much back pressure
    too big = not enough
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  13. #13
    Senior Member Three Rings
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    On a turbo car you cant have too big an exhaust. The back pressure all occurs in the exhaust manifold, turbine housing, and turbine itself. Once your past the turbo you want to get the gasses away as fast as possible.

    A 5" drainpipe sticking out the front wing would be about the best exhaust you could fit to a turbo 1.8T

  14. #14
    Veteran Member Four Rings BlackLock_A4's Avatar
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    Quote Originally Posted by turbo kraut View Post
    too small = too much back pressure
    too big = not enough
    1st statement is right, 2nd one - not so much. K03 is enough back pressure for the motor. However, if it's too big - the air will cool closer to the turbo causing more dense air where you don't want it.

    That isn't a back pressure effect.

    Sorry OP - I was surprised even google didn't have a diagram for you. lol
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  15. #15
    Veteran Member Four Rings BlackLock_A4's Avatar
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    Quote Originally Posted by Aragorn View Post
    On a turbo car you cant have too big an exhaust. The back pressure all occurs in the exhaust manifold, turbine housing, and turbine itself. Once your past the turbo you want to get the gasses away as fast as possible.

    A 5" drainpipe sticking out the front wing would be about the best exhaust you could fit to a turbo 1.8T
    Please read my post above. It isn't back pressure - it's the cooling of air. And you can have too big of exhaust.

    The last statement may be true because the air gets released in the atmosphere very quickly.
    2001 1.8TQM
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  16. #16
    Senior Member Three Rings
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    Ofcourse the turbo creates back pressure, its that very pressure that drives the turbine.

    After the gasses have driven the turbine, you want rid of them as quickly as possible, and that means as big a pipe as you can sensibly get in.

  17. #17
    Veteran Member Four Rings BlackLock_A4's Avatar
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    Quote Originally Posted by Aragorn View Post
    After the gasses have driven the turbine, you want rid of them as quickly as possible, and that means as big a pipe as you can sensibly get in.
    False. Why? Here is what I was trying to explain earlier:

    Here is a nice article I found. Read through it if you get bored. here
    From the article:

    "We've seen quiet a few "experienced" racers tell people that a bigger exhaust is a better exhaust. Hahaha… NOT.

    As discussed earlier, exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route. Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. Coating the entire exhaust system with an insulative material, such as header wrap or a ceramic thermal barrier coating reduces this effect somewhat, but unless you have lots of cash burning a hole in your pocket, is probably not worth the expense on a street driven car."


    There you go OP - sorry no diagram. lol
    I would say 2.5 - 2.75 would be fine for K03, although after the cat I don't think it will make a difference what size you go to - it's very restrictive.
    2001 1.8TQM
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  18. #18
    Senior Member Three Rings
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    Said article is mainly talking about naturally aspirated engines though.

    The turbine works by way of a pressure differential. The lower the pressure is on the exhaust side of the turbine, the more efficient it becomes. As such you can quite happily stick a huge pipe on there without worrying about pulse tuning or any other things you need to worry about on a naturally aspirated cars exhaust.

    That said, theres probably little to be gained from going bigger than 2.5" with the stock turbo, but a 3" pipe isnt going to hurt anything, and if your planning on fitting a larger turbo in future, its probably worthwhile going bigger now.

  19. #19
    Senior Member Two Rings
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    Quote Originally Posted by Aragorn View Post
    Said article is mainly talking about naturally aspirated engines though.

    The turbine works by way of a pressure differential. The lower the pressure is on the exhaust side of the turbine, the more efficient it becomes. As such you can quite happily stick a huge pipe on there without worrying about pulse tuning or any other things you need to worry about on a naturally aspirated cars exhaust.

    That said, theres probably little to be gained from going bigger than 2.5" with the stock turbo, but a 3" pipe isnt going to hurt anything, and if your planning on fitting a larger turbo in future, its probably worthwhile going bigger now.
    Well for this one that I have now I don't plan on going any bigger so would 2.5 or 2.75 be best you think? Was also thinkin about getting a LaBree hfc

  20. #20
    Forum Moderator Four Rings A4Rob's Avatar
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    Why don't you just look under your car? Buy some mandrel bent pipes online (variety) so you are prepared for anything when you make your setup.
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  21. #21
    Senior Member Two Rings
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    Quote Originally Posted by A4Rob View Post
    Why don't you just look under your car? Buy some mandrel bent pipes online (variety) so you are prepared for anything when you make your setup.
    I don't have a lift or anything to where I'd have a full view of the exhaust, and I'm not making the exhaust on my own I just wanted to know where everything was so I could determine on where I was going to have the exhaust shop straight pipe it. Also what happens if the exhaust is to big and there's too much back pressure?

  22. #22
    Senior Member Two Rings
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    Just get rid of the whole exhaust, that MUST make it the best exhaust in the world!!!
    Ive had a few beers!!!
    You can still flow a lot of gas volume down a 2.5in pipe. More than enough for k03/k04.
    The larger pipe diameter you go for a given mass of gas the slower this gas travels, thus the less momentum it has.
    This is what you want for a road car, good low and mid range torque. Or would you sacrifice that for maybe 3 or 4 hp right at the 5000rpm where you spend maybe 5% of the time?
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