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3.3TT Restrictive stock exhaust.....why?

Discussion in 'Engine, Drivetrain, and Exhaust Discussion' started by f155mph, Jun 28, 2018.

  1. f155mph

    f155mph United States Newish Member

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    Just got the car couple weeks ago and finally got a chance to look around on the underside. I have never seen a stock exhaust that have so many kinks that restrict flow. Does this car require a certain amount of back pressure?
     
  2. StungBlueGT2

    StungBlueGT2 United States Stinger Enthusiast

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    Great question and I initially wondered that myself.

    Without going into an in depth explanation, I've always understood that less back-pressure is better, especially for turbo cars. So no, the Stinger wouldnt required a specific amount of back-pressure.

    The kinks and restrictions were most likely used by Kia to help limit excessive sound & eliminate drone.
     
    Last edited: Jun 28, 2018
  3. DiabloStinger

    DiabloStinger United States Active Member

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    a free-er flowing exhaust adds a fair amount of power. always a good idea on FI cars.
     
    • Agree Agree x 1
  4. DaJackson

    DaJackson United States Stinger Enthusiast Staff Member Moderator

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    Go look at more modern OEM exhaust systems, they all have similar design elements. Reduces noise, allows for better clearance, etc.
     
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  5. Kazz

    Kazz United States 1000 Posts Club!

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    A certain amount of back-pressure, as I understood it, was good for torque. We have gobs of that. But yes, the OEM piping is almost Picasso-like in it's craziness of curves, angles, shaping of sections, etc. I can't even describe it.

    I do know that the crimps are for clearance. They want NO knocking of the exhaust on the car - and, of course, they never could have it the way they've done it. LOL
     
    • Funny Funny x 1
  6. Tonkabob

    Tonkabob United States Active Member

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    Need for back pressure is a myth. There are some good you tube vids doing dyno testing with all kinds if exhaust configs.
     
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  7. Mike04SVT

    Mike04SVT United States Member

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    Yes...For FI Cars
    Refer to above comment. In most cases non FI cars need back pressure.
     
    • Agree Agree x 1
  8. Jonathan Lasich

    Jonathan Lasich Canada Active Member

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    Normally aspirated engines--require some back pressure to retain low rpm torque.
    Forced induction engines--require no back pressure. The freer flowing, the better and the more power generated.
     
  9. eflyguy

    eflyguy United States 1000 Posts Club! Staff Member Moderator

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  10. Helo58

    Helo58 United States Active Member

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    Many people are ignoring the fact that the turbo itself is "back pressure." It is this pressure that determines the housing/turbo size and it also drives the turbo. Most turbo manifold/housing design is geared towards minimizing lag by having exhaust pulses reach the turbine blades at specific times. Once the exhaust has done the work on the turbine and exits the housing, you want the lowest pressure possible post turbine. Meaning that you upsize the exhaust diameter until no additional benefit is noticed. Simply put, back pressure doesn't matter for scavenging purposes in turbo cars and exhaust pressure should be as low as possible after the housing.

    It should also be noted that the term "back pressure" for NA cars is often misused or conflated with other things. Saying that back pressure isn't needed in normally aspirated (NA) cars all depends on what you mean by back pressure. Many professionals use the term "back pressure" to refer to the high or low state of pressure wave scavenging in the exhaust at the exhaust valve when the valve opens (back pressure #1). Others refer to it more generally to just mean internal pressure inside the entire exhaust system without referring to scavenging pressure waves (back pressure #2). Given both of these possible definitions, it is simultaneously possible to DECREASE exhaust system internal pressure (back pressure#2) while INCREASING scavenging pressure at the valve due to pressure wave changes (back pressure#1) for certain RPMs. A larger diameter exhaust is not always the answer, a "tuned" or engineered exhaust is.

    It is impossible (currently) to tune an exhaust system in such a way that the lowest pressure scavenging wave is always at the exhaust valve when the valve opens, but that is the goal. It is for this reason that tuned/equal length/long tube headers exist. Some strategies target high horsepower at specific RPMs and other strategies target a lower power gain but across a wider rpm band to increase drivability. Cars without an exhaust system or even collector (i.e. top fuel dragster) are not affected by exhaust system design. Only in the NA cars where exhaust gases are collected into common pipes are these elements critical.
     
    Last edited: Jun 29, 2018
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  11. Ecsta

    Ecsta Canada Newish Member

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    Most of the time they are designed for low cost and good emissions first, sound and performance second. At least it's a fairly cheap (comparatively) and super simple part to replace.
     
  12. niko

    niko United States Active Member

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    Will anyone remove the restrictions for more flow? A friend did it on gti Volkswagen and it gave him a better sound, I asked if any problems have occurred since he said no. What do u guys say doing it on the stinger
     
  13. eflyguy

    eflyguy United States 1000 Posts Club! Staff Member Moderator

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    I just wonder why they did this, as the aftermarket versions don't seem to have clearance issues...

    [​IMG]
     
  14. f155mph

    f155mph United States Newish Member

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    Thanks everyone for your input. Sounds like the consensus is to reduce sounds. That said I still think it is crazy to put restriction as shown in eflyguy pic where the muffler meet the main pipes.
     
  15. Andrew Simons

    Andrew Simons Member

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    Tork Motorsports did a video about the exhaust. After swapping exhaust and putting in a new K&N style intake he showed gains of 44HP at the wheels. The stock exhaust is indeed hindering performance and 44HP seems well worth a swap to me. If you are going to do other bolt ons/tune it would make an even larger difference.
     
  16. BurwellStingerGT

    BurwellStingerGT United States New Member

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    I wonder how much of a gain it would be to simply cut that small crushed section on each side and weld in a straight section?
     
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