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Who is right??

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by chevy4x4, Sep 3, 2000.

  1. chevy4x4

    chevy4x4 1/2 ton status

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    Ok, 84K5 and me were having a little debate in the chat room. I say big mufflers restrict airflow and he says small ones do. Who is right?

    [​IMG]
    [​IMG]K5[​IMG]
     
  2. jcg

    jcg 1/2 ton status

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    A muffler that is too large will restrict the flow more than a smaller one with the same internal design. The sudden increase in volume will create a huge pressure increase which lowers the velocity of the gas. This is why straight pipes give better performance than a system with mufflers. Of course this is only true for a system that doesn't use fuel injection, which requires the back pressure from a muffler for top performance.

    Joe
    Rochester Institute of Technology Team Mini-Baja
    88 Jimmy
     
  3. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    both...ALL mufflers restrict air flow to some extent. Anything the pipe changes diameter it creates turbulance and slows the flow down. Even a glass pack will have this effect because the walls are perferated and will still create turbulance. The size has nothing to do with the amount of restriction it's the flow pattern that does. A Flow master is a pretty good size muffler and it has one of the lower flow resistance on the market.

    Diging it in the dirt with my K5's
    Grim-Reaper
    http://grimsk5s.coloradok5.com/
     
  4. 82Jimmy

    82Jimmy 1/2 ton status

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    just weld dumps on after the headers, no air restriction there! [​IMG] or heak just put some headers and no pipes! I think the big ones will restrict a lot more. Not an expert, but thats my opinion

    <font color=blue>If its too loud, your too old.</font color=blue>
    http://82Jimmy.coloradok5.com
     
  5. realsquash

    realsquash 1/2 ton status

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    The size of the muffler has nothing to do with it's flow and EFI doesn't require backpressure to work correctly. Placement of the muffler and the type of muffler has the largest effect. You will get less restriction if the muffler is really far back in the system than if it is right after the headers because the cooling exhaust gas will have less volume and therefore require less "room" to move.

    Squash
    http://www.trailrunners4x4.org/users/realsquash
     
  6. jcg

    jcg 1/2 ton status

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    I was always told that EFI systems needed a certain amount of back pressure (provided my the cat) to work right... it never made much sense to me but I just went a long with it. I think I was told that because at the time I was going to slide a pipe through my cat and put on Flowmasters. I guess it's time to get a new exhaust system! [​IMG]

    Joe
    Rochester Institute of Technology Team Mini-Baja
    88 Jimmy
     
  7. jcg

    jcg 1/2 ton status

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    Almost forgot... now that I really think about it, your right. The size of the muffler wouldn't matter, it's just the exit and entrances of the pipe that cause the energy loss in the flow compared to a straight pipe (if you ignore the baffles). I've been painting my truck this week so the hampster upstairs has been a little slow from the fumes [​IMG]. I know about the placement of the muffler, I just didn't mention it because the question only asked about the difference between sizes, and well... you get the idea. Wow, I really think I need new filters for my respirator.

    Joe
    Rochester Institute of Technology Team Mini-Baja
    88 Jimmy
     
  8. turbo

    turbo 1/2 ton status

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    All normally aspirated engines FI or carb need some back pressure for low RPM power.
    However turbocharged engines get suficient backpressure from the turbocharger and no aditional restriction is needed for low end.

    Dont believe me just put a header and straight 3 or 4" straight pipe on your FI 350 and watch how much low end you loose.
     

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