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  1. #13
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    Quote Originally Posted by dillon.ornelas View Post
    no, im not stupid enough to drive a car in Australia without an exhaust lol, the whole point of this thread is to attempt to answer the question, will back pressure from an exhaust give you more power, from the evidence i can gather, the exhaust back pressure loses you power, back pressure in the headers is important for scavenging and can utilized to gain power.

    sorry if i have stepped on people toes or people have lost the point im trying to make

    is a giant exhaust good for the street? only if we lived in a world where we were all deaf
    will a giant exhaust loose you power? only if you motor doesn't have a well designed header/extractor.

    i honestly WANT to see a dyno that proves back pressure will show a gain somewhere on some motor
    Numbers aren't everything. My experience was the car felt much better going from 3inch to 70mm. Sure, 3 inch probably makes more numbers, but i enjoy driving my car and value the driving experience more then the print out from the rollers.

    I find it funny reading interviews with Japanese tuners and reading interviews with american tuners and how they both have conflicting ideas/methods.

    http://www.hybrid-racing.com/blog/ja...ngine-service/

    Long read, but you will understand what I'm saying when you get to the end.
    BONUS ROUND
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  2. #14
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    Its not really about empirical evidene here... Go study some basic fluid dynamics.

    You dont see us harping on about backpressure here...

    Cos theres no such thing as backpressure.
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  3. #15
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    Okay, Then why is the principle seemingly hard to apply?

    According to bernoulli, faster exhaust gas = lower presure in the pipe (and therefore less backpressure)

    So for a given flowrate (Q), there will be an ideal velocity which is directly related exhaust size. As Q is related to engine speed, a a givenexhaust size will not favour all engine speeds. This is why bigger exhausts produce more power on a dyno (producing torque at high rpm gives more power which isnt always useable)

    You also seem to be correlating backpressure to exhaust size, this isnt necessarily correct
    S P A M | W O R K S
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  4. #16
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    Quote Originally Posted by dillon.ornelas View Post
    it raised more questions than it answered
    to start the fluid we are dealing with isn't ideal (one which is in-compressible and has no viscosity) then we have to deal with the fact that flow is unsteady and at times not laminar (it comes out in pulses)
    then we have to deal with head losses, losses from fluctuating temperature, expansion and contraction, friction and turbulence from bends, surface imperfections and viscosity. (there is probably more that im forgetting).
    hence why f1 designs headers with trial and error (the people who make them are very experienced) and why every year they look completely different.
    You were asking specifically about sizing, not about head loss due to bends and temperature loss

    these cant be avoided with the design of a streetcar
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  5. #17
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    OoOoOoOoOoOoOoOoOoOoOoOo!!!!!!!!
    Last edited by joyride; Today at 07:26 AM. Reason: Ask for permission if you're going to use someone elses pic

  6. #18
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    Yes thats correct but still does not necessarily quantify a larger vs smaller exhaust, that comes down to rigorous lab testing i suppose.... Which is whst you seem to be alluding to

    I thougbt u were being the usual backpressure potato
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  7. #19
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    Its ok we're not all potatoes on here
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  8. #20
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    I know what laminar/turbulent means...
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  9. #21
    this thread makes me


  10. #22
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    Quote Originally Posted by dillon.ornelas View Post
    lol "backpressure potato" when ever someone calls someone else a potato i giggle like a school girl. (its sad, im telling the truth)
    i know its not real. the term back pressure has never come up in fluid dynamics text books ONCE. NEVER. i honestly never thought i would have to get so technical on an online forum.
    So are you giving this knowledge/advice on your own research and YOUR REAL WORLD TESTING or just crap you have read in text books and the web ?
    The life of a 4 stroke engine
    It sucks it squeezes it bangs it blows

  11. #23
    Quote Originally Posted by ALLMTR996 View Post
    So are you giving this knowledge/advice on your own research and YOUR REAL WORLD TESTING or just crap you have read in text books and the web ?
    He (the thread starter) sounds like a disgruntled 1st year student - all book smart and no real world knowledge. No offence OP - but you sound like you are directly quoting wikis / other net resources with info but you clearly do not understand yourself.
    Last edited by bennjamin; 26-08-2013 at 03:16 PM.

  12. #24
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    No wiki's or net info here just many years of dyno knowledge on what works best on Honda setups.
    The life of a 4 stroke engine
    It sucks it squeezes it bangs it blows

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