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What is inside the airbox?

Discussion in 'XJ Technical Chat' started by Bryce W, Nov 19, 2022.

  1. Bryce W

    Bryce W Member

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    Hey y'all just a quick question. I got an airbox from a 700 airhead that Ive just installed on my 85 maxim x 700. I was wondering, there is a long, oval, tubular piece of rubber/plastic that fits into the opening of the airbox. It looks like it acts as a huge restriction/ has some sort of intake effect? Any thoughts on what this does, or is it some sort of air intake velocity stack. What if I don't use it?
     
  2. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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    They call these a “duct”. I assume they are intended to smooth out the airflow something like a velocity stack, but I don’t really know.

    My idea would be to try it with and without and see if you can notice any difference.

    whatever you do, don’t just toss it in the trash. At least keep it.
     
  3. tabaka45

    tabaka45 Well-Known Member

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    Put it in. Keep the bike stock.
     
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  4. cgutz

    cgutz Well-Known Member

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    Concur on keeping it stock.

    I am amazed how many try to tweak the XJ's for better performance. The competition for power/speed was really great in the 80's, and the company engineers likely knew what they were doing...
     
  5. Bryce W

    Bryce W Member

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    Yeah the consensus for the bikes is keep them stock... Just wanted to know what it did for airflow
     
  6. Bryce W

    Bryce W Member

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    Just talked to my dad, he said they put those in the intakes to quiet the intake noises.
     
  7. Minimutly

    Minimutly Well-Known Member

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    Maybe, but what’s not obvious is that the air box is a tuned volume, a resonator if you like. You take that snorkel out and any boosts from the resonant frequency is lost.
    Also, the air box and filter gives a known restriction, which the carb springs and slides are set to - you will also lose this.
    The upshot is likely to be lost performance, so keep the snorkel thing.
     
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  8. Bryce W

    Bryce W Member

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    Agreed!
     
  9. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    If there were a "love" option I'd click it.
    It really annoys me how many people are entirely ignorant of the engineering the goes into airboxes. Even the relatively primitive engineering that was done in the 70's and 80's.
     
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  10. Minimutly

    Minimutly Well-Known Member

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    To be fair Yamaha were experts in musical instruments, so would have not been unfamiliar with air pressure and sound waves. The 600 airbox on my 650 maxim has a helmholtz resonator on the side - these didn't appear on cars untill the 2000's.
     
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  11. jason191918

    jason191918 Member

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    i always thought it had to do with water...any water would be forced to the bottom drain and not into the filter.
     
  12. Minimutly

    Minimutly Well-Known Member

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    No. Neither here nor there. Except that Oem paper filters don’t like water
     
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  13. Bryce W

    Bryce W Member

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    No filter likes water, more water means more resistance means rich carbs. One thing is for sure, this one little part has many logical explanations as to why it was included!
     
  14. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Having ridden through a few thunderstorms I can attest to the fact that water cannot enter the airbox unless one chooses to put it there.
     
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  15. Huntchuks

    Huntchuks Well-Known Member

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    Yep, no water in airbox here either, but it was everywhere else
    20220612_150349.jpg
     
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  16. Bryce W

    Bryce W Member

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    Boy you had that X loaded up!
     
  17. Franz

    Franz Well-Known Member

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    On his way back from the Carb Clinic l think.
     
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