Reducing header outlet

Discussion in 'Exhaust' started by Poolio, May 4, 2019.

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  1. May 4, 2019 #1

    Poolio

    Poolio

    Poolio

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    What effect would reducing header outlet from 2.25” to 2” have on the bike? Trying to find a slip on and it’s next to impossible to find a 2.25 inlet. Plenty of 2”. I just don’t want to hurt the bikes performance.
     
  2. May 4, 2019 #2

    sandy klock

    sandy klock

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    You might make more hp with the 2". My 96 made 133hp with 2" less with 2.5".
     
  3. May 5, 2019 #3

    Fire-medic

    Fire-medic

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    I'm no flow dynamics engineer, but I presume that any restriction in diameter should be a gradual blending of the circumference of the larger into the smaller. By doing this you're allowing for an increase in the flow rate while below the threshold of what is the maximum flow for that density, that pressure, and that friction/resistance generated. Done correctly the velocity of the gases increases, up-to the maximum velocity for that density. Done incorrectly, you introduce all-sorts of turbulence into the flow, interfering with the passage of the liquid or gas.

    I recall one of the things which allowed Harley-Davidson to be successful with their flathead KRTT engine was a reduction in the port size, which promoted an increase in intake/exhaust gases velocity, better scavenging, and more HP. Jerry Branch, he of what became Branch Flowmetrics, and I think Bill Werner, HD mechanic for their race team, with Dick O'Brien of HD management, were able to keep the flathead competitive while the OHV XR 750 was being pushed-through development. This was the very-early 1970's.
     
    Last edited: May 5, 2019
  4. May 5, 2019 #4

    sdt354

    sdt354

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    133 hp is high for a stock Gen 1. Or even one with stage 7 and aftermarket exhaust system. What mods were done on that engine? Chain drive?
     
  5. May 5, 2019 #5

    VMAXXIMUM

    VMAXXIMUM

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    Maybe he's referring to his crank hp?
     
  6. May 5, 2019 #6

    sdt354

    sdt354

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    That would be quite low, for an import, anyway Bro.
     
  7. May 5, 2019 #7

    sandy klock

    sandy klock

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    Stock engine with shaft drive, Kerker, individual filters needles and Good jetting. Stage 7 costs hp. Bike made 131 and addition of 17" gsxr wheel was 2.5hp full length of pull for 133+. Probably weight savings and maybe hooking up better on drum. Maybe alittle bit of gear reduction too. Bike ran high 10,s @800' above sea level.
     
    Last edited: May 6, 2019
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  8. May 6, 2019 #8

    one2dmax

    one2dmax

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    We have made 132/133 on a few bikes with both being high mileage examples. It can be done.
     
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  9. May 6, 2019 #9

    Poolio

    Poolio

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    It just allows me a lot more can options. 2.25 inlet is a pain in the ass to find. Almost as hard as 4” 18 gauge carbon fiber tubing. Or as hard as bleeding those new six pots with a hammer. Thanks for the great brakes and advice along the way Sean and others. Turning my vision slowly into reality. Just got the rear gold pot. I’m sure I’ll be ordering your bracket in a few weeks.
     
  10. May 6, 2019 #10

    sdt354

    sdt354

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    Some good tuning there. Sorry I hijacked your thread Poolie.
     

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