Wrapping pipes increases exhaust flow?

Discussion in 'Sportster Models' started by RiffRaff, May 13, 2010.

  1. RiffRaff

    RiffRaff Member

    9
    11
    0
    I just read Ranger63's thread asking whether or not he shoud wrap pipes. Some of the replies mentioned that doing so helps exhaust flow. That baffles me (no pun intended). Can anyone explain how that happens?
     
  2. Jack Klarich

    Jack Klarich Expert Member

    18,544
    153
    399
    Helps to create low pressure for better scavenging IE better flow, but wrapping hold moisture in and can ruin the exhaust, you decide:p
     
  3. larryjmiller

    larryjmiller Junior Member

    448
    26
    0
    Say what????
    I suppose if you were wrapping them on the inside. The velocity would increase with a decrease in pressure...you decide. Consider a physics class, I know a good teacher.
    [​IMG]
     
  4. Jack Klarich

    Jack Klarich Expert Member

    18,544
    153
    399
    This is a racers edge look at Pro Drag bikes and tell me what you see:)
     
  5. nakkers

    nakkers Active Member

    393
    28
    6
    Jack,

    You were close. It's the magic of heat, not pressure.

    The hotter the exhaust gas in the header, the less dense it will be. Thus, improved/better scavenging. (The wrap helps keep the heat in)

    I'm sure that's where you were going with this.......:s

    At least that's the theory.

    Is it practical for a street machine? I don't think there would be any noticable difference. Other than having "the look". That and having the desire to replace the exhause on a frequent basis.

    Or I guess if someones exhaust system is looking a bit tired and they want to cover it up for a season? They are only prolonging the envitable to replace it.

    Jack,

    You're still right. And I need to stop reading this forum while I pretend to watch my children. I'm not doing either very well.

    Reduced desensity of exhaust gases i.e. lighter.......requires less effort to expell.........less pressure.........



    Back to the kids. My apologies..........
     
    Last edited by a moderator: May 15, 2010
  6. Jack Klarich

    Jack Klarich Expert Member

    18,544
    153
    399
    Greater heat retention= higher gas velocity at least according to The Big Twin High Performance Guide:p
     
  7. murf

    murf Active Member

    322
    0
    1
    Nakkers nailed it, cold dense air moves slower. Wrapping the pipes keeps the air warmer all the way out the pipes, therefor moving faster. I'm still not convinced, however, that wrapping retains moisture and corrodes pipes ...unless you are taking repeated short runs and not getting pipes warm enough to get rid of condensation.
     
  8. glider

    glider Veteran Member

    25,464
    108
    44
  9. NEWHD74FAN

    NEWHD74FAN Experienced Member Retired Moderators

    8,176
    98
    16
    Wrapping pipes is a racer trick...and the pipes need only last 'till the weekend "2 to 3 days of hard riding, then it is over...remembering that racing teams are well funded...not made for long term use. As mentioned earlier in the previous post, Hobbit ran them on his 'Bob and probably more like a scalded dog, once out in his "top secret" riding location. While cold and wet is common weather "-merry old" I still say a couple years of hard use is not good enough for "practical use" for a street rod.
     
    Last edited: May 14, 2010
  10. rancid

    rancid Active Member

    257
    28
    1
    the heat wrapping doesnt hold moisture in, it holds more heat than the metal can withstand which causes the metal to oxadize, i dont think an exhaust can have anything cause moisture to be retained other than washing the bike then not getting it hot but most pipes are chrome plated which will stop any corrosion due to moisture. look at exhust flange studs on an old car engine, they oxadize and go brittle due to heat cycling. the only thing it will do on a street bike is wreck the pipes. the racing industry doesnt use it any more either the ceramic coatings are the most reliable way to manage heat in an exhaust system.