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Back Pressure Question

Discussion in 'Performance and Tuning' started by Drunknsloth, Jan 11, 2011.

  1. Jan 11, 2011 at 11:11 AM
    #1
    Drunknsloth

    Drunknsloth [OP] Indffrnce will be the fall of manknd but who cares

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    So I've been reading a few threads on exhausts and people keep saying things about backpressure. It seems that people think that you need more backpressure, but I thought you only needed backpressure, and a small amount at that, if you had a turbo. So I looked it up and found this website: http://www.thumpertalk.com/forum/showthread.php?t=659727 which explains that you want zero backpressure with the highest output velocity of exhaust gases. Sooo... According to this website, a cut out with the right diameter pipe would be the best choice for performance as to have close to zero backpressure and with the highest output velocity of exhaust gases. So in theory this increase in efficiency should also increase your miles per gallon right?

    Does everyone who complains about loosing back pressure actually mean loosing the velocity of output? Because you don't want back pressure right?

    Am I wrong or does this make sense?

    Edit: According to further reading, you do not want back pressure on turbos either :confused:
     
  2. Jan 11, 2011 at 2:57 PM
    #2
    Speed Freek

    Speed Freek Turbo Meister

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    You do not want ANY BACKPRESSURE in any forced induction application, even in NA vehicles you want the proper scavenging effect, which seems to get lost in translation...
     
  3. Jan 11, 2011 at 3:00 PM
    #3
    sethr21785

    sethr21785 Well-Known Member

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    no backpressure on turbos is fine but on a NA you want some backpressure..
     
  4. Jan 11, 2011 at 3:42 PM
    #4
    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Thor

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    Bingo!
     
  5. Jan 11, 2011 at 3:46 PM
    #5
    ToucanV13

    ToucanV13 You think I was rollin out here naked?

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    What if you're not boosted though?
     
  6. Jan 11, 2011 at 3:47 PM
    #6
    whippersnapper02

    whippersnapper02 Well-Known Member

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    On turbo vehicles backpressure really isn't needed since the momentum of the turbo will suck out exhaust gasses from the cylinder. Any backpressure in the system just reduces the turbo's efficiency.
     
  7. Jan 11, 2011 at 3:48 PM
    #7
    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Thor

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    Back pressure is bad regardless. Scavenging is what is used to get the most HP/TQ out of an NA engine. Scavenging doesnt play as much of a role when FI.
     
  8. Jan 11, 2011 at 3:53 PM
    #8
    ToucanV13

    ToucanV13 You think I was rollin out here naked?

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    So a cut out would be beneficial even in a stock engine application...
     
  9. Jan 11, 2011 at 3:54 PM
    #9
    whippersnapper02

    whippersnapper02 Well-Known Member

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    At high RPM only.
     
  10. Jan 11, 2011 at 4:29 PM
    #10
    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Thor

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  11. Jan 11, 2011 at 4:31 PM
    #11
    BrokenTusk

    BrokenTusk I support a velociraptor free workplace.

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  12. Jan 12, 2011 at 9:09 AM
    #12
    Drunknsloth

    Drunknsloth [OP] Indffrnce will be the fall of manknd but who cares

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    But according to the website, the where in the RPM range you get more power depends on the size of the pipe...
     
  13. Jan 12, 2011 at 11:55 AM
    #13
    ToucanV13

    ToucanV13 You think I was rollin out here naked?

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    So how would you benefit more from a 3" as opposed to a 2.5" or is it marginal and only a racer/high performance car could notice a difference. I understand a bigger pipe allows more air flow but I want to know if it's marginal
     
  14. Jan 13, 2011 at 9:16 AM
    #14
    Drunknsloth

    Drunknsloth [OP] Indffrnce will be the fall of manknd but who cares

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    From what I learned from the website it depends on what RPM range you want more power at. If you go for a 3" the velocity of the exhaust will be slower at low RPM range and faster at a higher RPM range. If you go with a 2.5" the increase in power would be at a lower RPM range then the 3"
     
  15. Jan 13, 2011 at 9:37 AM
    #15
    whippersnapper02

    whippersnapper02 Well-Known Member

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    Yup. The larger the pipe the small amout of backpressure so the less amount of exhaust scavenging. Your gain top end but lose low end.
     
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