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    Thread: 2.25" exhaust enough?

    1. Member docterelliott's Avatar
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      04-11-2012 02:31 AM #1
      I plan on keeping my stock exhaust size but putting a 3" catless DP in and im only running a stage 1 chip w/ a k03 sport turbo right now. if I ever wanted to go with a bigger turbo and more boost would the 2.25" exhaust be adequate or would a 3" exhaust really make a significant difference?

    2. Moderator groggory's Avatar
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      04-11-2012 02:54 AM #2
      Quote Originally Posted by docterelliott View Post
      I plan on keeping my stock exhaust size but putting a 3" catless DP in and im only running a stage 1 chip w/ a k03 sport turbo right now. if I ever wanted to go with a bigger turbo and more boost would the 2.25" exhaust be adequate or would a 3" exhaust really make a significant difference?
      a 2.5" exhaust would net you gain right now. A 2.25 isn't a monster restriction though.

      a 3" isn't necessary til you're on the larger side of k04 or larger.
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    3. Member docterelliott's Avatar
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      04-11-2012 03:10 AM #3
      really? even with just an itty bitty k04 you need a 3"er? i had planned on throwing in a magnaflow resonator and muffler with the stock piping. that would basicaly be straight pipe from the turbo back to the muffler. with those included would my theoretical exhaust setup work efficiently for what I have or maybe even for the k04?

    4. Moderator groggory's Avatar
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      04-11-2012 03:48 AM #4
      Quote Originally Posted by docterelliott View Post
      really? even with just an itty bitty k04 you need a 3"er? i had planned on throwing in a magnaflow resonator and muffler with the stock piping. that would basicaly be straight pipe from the turbo back to the muffler. with those included would my theoretical exhaust setup work efficiently for what I have or maybe even for the k04?
      No.

      2.25 is weak sauce

      2.5" min piping

      3" down pipe for sure

      Stock cat is fine
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    5. Member Big_Tom's Avatar
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      04-11-2012 05:16 AM #5
      Quote Originally Posted by groggory View Post
      a 2.5" exhaust would net you gain right now. A 2.25 isn't a monster restriction though.

      a 3" isn't necessary til you're on the larger side of k04 or larger.
      yup, i'd run 3" from the get tho. even on a k03s thats bette than 2.25 or 2.5" for making power
      My Thread Fk AK Coilovers, Full 3" Exhaust, Custom FMIC, Forge Evo14 BOV, Forge Unos MBC, Forge Throttle Body Hose, Prothane Dog Bone Mount, BFI STG 1 Eng/Trans Mounts, Sachs VR6 Clutch Kit, TT Short Shifter, Siemens 630s, Walbro 255, DBB Garrett 50 Trim Turbo Kit, Eurodyne 630cc MAFLESS PAGPARTS FTW -- STEVEBILT.COM -- Integrated Engineering -- FourSeasonTuning.com Don't Buy Anything From *ChunkyPeanuts*

    6. Member docterelliott's Avatar
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      04-11-2012 11:24 AM #6
      your saying the 2.25 exhaust is a significant restriction compared to the 3" but correct me if Im wrong but wouldnt the stock cat be even more of a major restriction?

      have you guys run a 3" exhaust with the stock k03? did it move the power curve? I heard a full 3" turbo back with a small turbo will kill all your bottom end power? thats needed for a smooth daily driver
      Last edited by docterelliott; 04-11-2012 at 11:26 AM.

    7. Moderator groggory's Avatar
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      04-11-2012 01:19 PM #7
      Quote Originally Posted by docterelliott View Post
      your saying the 2.25 exhaust is a significant restriction compared to the 3" but correct me if Im wrong but wouldnt the stock cat be even more of a major restriction?

      have you guys run a 3" exhaust with the stock k03? did it move the power curve? I heard a full 3" turbo back with a small turbo will kill all your bottom end power? thats needed for a smooth daily driver
      Turbos work best with zero back pressure.

      The engine needs a little back pressure to operate efficiently down low...but you have a little k04 turbine to provide all the back pressure for the engine.

      Behind that turbine it's all about temperature and pressure differentials. The larger the differential, the faster the exhaust wants to flow through the turbo...and the harder you boost and the more power you make.
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    8. Member Big_Tom's Avatar
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      04-11-2012 01:58 PM #8
      Quote Originally Posted by docterelliott View Post

      I heard a full 3" turbo back with a small turbo will kill all your bottom end power?
      somebody told you wrong
      My Thread Fk AK Coilovers, Full 3" Exhaust, Custom FMIC, Forge Evo14 BOV, Forge Unos MBC, Forge Throttle Body Hose, Prothane Dog Bone Mount, BFI STG 1 Eng/Trans Mounts, Sachs VR6 Clutch Kit, TT Short Shifter, Siemens 630s, Walbro 255, DBB Garrett 50 Trim Turbo Kit, Eurodyne 630cc MAFLESS PAGPARTS FTW -- STEVEBILT.COM -- Integrated Engineering -- FourSeasonTuning.com Don't Buy Anything From *ChunkyPeanuts*

    9. Member flood514's Avatar
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      04-11-2012 02:05 PM #9
      A quote from my exhaust guys website about exhaust system sizing . I found it interesting.

      "Choosing performance exhaust can be confusing. A common misconception is that "bigger is better". Many enthusiasts feel that larger diameter pipes are the only way to go for car performance, but at Federal Mufflers, we have found for street use, the wrong diameter pipes just take energy out of the exhaust, both by slowing down exhaust gas velocity and by cooling its gases. While exhaust may leave the headers at 1500 degrees or more, at the tailpipe it’s down to 150 degrees -- a sign that energy has been lost. Velocity and uninterrupted flow are the real performance-making factors.

      It is the low frequency range that has energy (the sound you can feel inside the car); big pipes increase the low frequencies, making an uncomfortable roaring or droning sound. We design our exhaust system for less restriction, keeping the velocity and frequency high so the main sound is behind the tailpipe. Late model cars and trucks are computer controlled to such an extent that it may take a period of time (400-600 km) before the computer reprograms to reflect the improved flow of the new system. "

      The old hot air is lighter to push than cold air. As for the balance for individual setups...

    10. Member Big_Tom's Avatar
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      04-11-2012 02:17 PM #10
      buy what you want. you don't see small exhausts on race cars LMAO i have yet to see a truely fast car with a 2.25" exhaust
      My Thread Fk AK Coilovers, Full 3" Exhaust, Custom FMIC, Forge Evo14 BOV, Forge Unos MBC, Forge Throttle Body Hose, Prothane Dog Bone Mount, BFI STG 1 Eng/Trans Mounts, Sachs VR6 Clutch Kit, TT Short Shifter, Siemens 630s, Walbro 255, DBB Garrett 50 Trim Turbo Kit, Eurodyne 630cc MAFLESS PAGPARTS FTW -- STEVEBILT.COM -- Integrated Engineering -- FourSeasonTuning.com Don't Buy Anything From *ChunkyPeanuts*

    11. Member flood514's Avatar
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      04-11-2012 04:16 PM #11
      For my F4L I went with 3" test pipe to 2.5" the rest of the way. If I had planed to go with a bigger turbo one day I would have gone 3" the whole way. I'd say to the OP if you really want the system to be scalable for large turbo later just go full 3" now.

    12. 04-11-2012 04:30 PM #12
      I have a 3" catless dp that goes into stock exhaust with factory res, but with muffler deleted.

      It sounds amazing!!!! And when I go to the track I run open dp. Loud as all Hell, but definitely gives me some ponys

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      04-11-2012 05:25 PM #13
      That little snippet about pipe sizing is based on NA cars. You need to think about exhaust tuning with NA because too big will kill the low end tq. But as mentioned the backpressure that they need in the NA world is substituted by the turbocharger in the TC'd world. As mentioned bigger IS better on turbo'd cars. Plus with a K04 based turbo you will never be in need of low down tq it is all tq to begin with.
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    14. Member docterelliott's Avatar
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      04-14-2012 10:56 PM #14
      sweet good input. guess I will just go with 3" TBE

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