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Custom Airbox

Discussion in 'XJ Modifications' started by sebwiers, Dec 5, 2012.

  1. sebwiers

    sebwiers Active Member

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    After setting up a lot of other mods, I don't like the look of the airbox on my bike. However, I also don't like the hassle I hear comes with pods, and do like a nice heap of low end tuned torque.

    My idea is to build a custom airbox that has the same runner dimensions and volumes, just configured a bit differently. Any reason this change would affect performance adversely?

    Also, I'd like to switch the filter so that it fits OVER the snorkle, and use a conical "cold air" automotive filter. Again, any impact on tuning?

    The end setup would be this:
    filter-> snorkle -> volume that matches colume of stock airbox (plus filter holding portion) -> tubes that run into carbs with same dims as stock

    My understanding is that the purpose of the airbox is to act as a Helmholtz resonator, so if I maintain the same resonance by preserving the volume, neck cross section, and neck length, I should be good. I think a lot of the internal complexity of the airbox is just to make it structurally sound, keep oil away from the intakes, etc, and doesn't affect resonance at all.

    Is this sound thinking? If it is, I may have a spare airbox for sale when I get done...
     
  2. thechuck

    thechuck Member

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    hello. great question. I am planning on building a custom airbox for my xj550 project. I plan to use same rubber boots, similar inside volume box and foam style filter. also I will not be using a lid. I'm under understanding it's volume that dictates proper function of carbs. any more input would be great. also tinkering with idea of going constant velocity carbs. and foam pods.
     
  3. Orange-n-Black

    Orange-n-Black Well-Known Member

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    Streetbrawler750 made some velocity stacked pods that are similar to what you described. Others have made pvc intakes with some success and many different styles. One guy made a Maltese Cross shaped airbox for his bike but didn't show a decent pic of it.
    Making your own box shouldn't be too difficult or you could look on ebayfor an original. Some members on this site may have a box to sell, just make a WTB post in the for sale & trade forum.
     
  4. paul.hardy

    paul.hardy Member

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    I Have been down the road of air boxes and PODS on my XJ750 put pods straight on made extended velocity stacks put cowling around pods. Bike never ran quite right unfortunatly I cut my air box up. In the end I made up what I call an air intake manifold out of PVC plumbing pipe and just used one POD and now the bike actually runs better than with a standard air box however the bike did have 4 into 1 ex on it so extra air from the non standard air filter might have been needed. I am no expert but the biggest issue with thease side draft multipal carbs on these motors anyway, and PODS is that they don't allways (PODs) maintain equal air pressure across all 4 venture's. I think the air pressure or vacum at the venture affects the main jet slides operation so if theydo not open the same the bike will run crap. I apoligise to the carb experts on this site if I have this wrong.

    Can PM you picks of manifold and tips on how I made it if you like( I cant seem to work out how to upload picks to this site yet)
     
  5. Lewis

    Lewis Member

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    Share! Please share! :wink:

     
  6. thechuck

    thechuck Member

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    mos def on the custom airbox pics! not to add any fuel to the fire but i too have been down the pod road. tried everything from velocity stacks, air restricters, and all aorts of jetting combinations. don't get me wrong, bike pulled ok and looked stellar, and not even havve to say how easy it became to work on them. but, i put on stock airbox w/out lid and reg. filter, also lil fatter pilot, and that thing pulls to 9.5k w/out hesitation. this was on my xj650 seca. just sayn. we got a great used parts barn here in nh called coopers. i have been snagn wishlist parts for my 550 custm build, and plan to maybe grab some constant velocity carbs from dif. model (research involvd, lol).
     
  7. Orange-n-Black

    Orange-n-Black Well-Known Member

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    The original carbs on these XJ's are constant velocity carbs( have little dome shaped hats on top). Constant velocity carbs don't like air or exhaust mods and the YICS ports don't help either.
    Kehein CR's are great, but costly. Hard to find a rack of different carbs that have the same spacing as the XJ.
    A couple of guys have done the EFI conversion, but that can be difficult and costly as well.
    I did a 2 round slide carb conversion for about 500 bucks, but that required fabbing some custom intake manifolds.
     
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  8. sebwiers

    sebwiers Active Member

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    Sounds similar to my case. I still have my (undamaged) stock airbox, but I don't have the stock exhaust (got a 4-1, probably the same one as you).

    I plan to run one of those automotive cold air intakes mounted on the back of the airbox I build, so it looks like the bike has one (gigantic) pod! I don't have any side covers but I managed to relocate ALL the electronics AND the battery to be under my tank (its a Virago tank, has a much larger tunnel), so it should be rather eye catching. If it doesn't work out well, I CAN switch back to 100% stock carb config.
     
  9. RickCoMatic

    RickCoMatic Active Member

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    The Carbs we have on our Bikes are C-V Carbs.
    "Constant Velocity"
    The Intake Air entering the Carbs Intake Horn needs to be accelerated by traveling through a constricted space.
    Velocity Stack.
    That''s what the Airbox Rubber Boot does.

    The rapid column of Air entering the Intake Horn is necessary for:
    • Reducing Pressure at the Emulsion Tube exit orifice creating the condition that draws Fuel up into the Air Stream.

    • Reducing Pressure at the Diaphragm Pistons Bottom Orifice creating the Vacuum that deflates the Diaphragm lifting the Needle Valve as the Piston rises.
     
  10. thechuck

    thechuck Member

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    i lay more confused than i thought. i know this is a tread lightly suject and certainly dont want to go down that road. i tried hard to get same power characteristics; using all sorts of combinations in velocity stacks, filter material, tubes and jets. i would say i took "pods" head on, and regardless- that stock airbox pulls harder and a hell of a lot easier. i tracked ploblem down to what many of you have said; the air was rushing by emultion tube too quickly as to promote proper burn of fuel. im certainly leaning towards custom airbox. thanx so much for shedding more light on subject and fixing my ignorant ways. :). i also want to say that i have learned so much from reading your words and thank you
     
  11. sebwiers

    sebwiers Active Member

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    Yep. Like I said, planning to mimic their length and profile in my new airbox. Or I might just use the rubber units I have, to save time; if the new airbox is easy to remove, I'll be free to replace them later.
     
  12. RickCoMatic

    RickCoMatic Active Member

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    Eventually, the problem to overcome is a Lean Condition caused by Main Jet Supplied Fuel not being Siphoned into the Intake Air Volume in sufficient quantity do to the Intake Stream not being shaped and accelerated enough aas it passes over the Top of the Emulsion Tube to Siphon the Main Jet Fuel up the Tube.

    The condition is further exacerbated because the Turbulent Intake Air fails to reduce pressure at the Diaphragm Piston Orifice reducing the extraction of the Needle Valve from the E-Tube.

    Also, ... it is likely that the Flow of Intake Air --> across the Kidney-shaped Atmosphere Vent at the Top of the Intake Horn causes a REDUCTION of Atmosphere in the Void surrounding the Diaphragm Rubber, ... thereby starving the MAIN AIR Jet of sufficient AIR to vent down to the cavity supplying the needed AIR to bleed through the Holes drilled in the E-Tube to assist in the siphoning process.
     
  13. thechuck

    thechuck Member

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    jeez rick, your the man. i can feel your knowledge flexing from here. 8O sebwiers, you got the right idea; stock rubbers into custom airbox. the rubbers will look right, be easy to remove/mount, and they are already made. have you have a modified space that that box is going in? i purposely built space into my custm frame; having a feeling all along that i would be going airbox.
     
  14. sebwiers

    sebwiers Active Member

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    Yeah, I've modified it. All the electronics (battery included) will be entirely out of view (under the tank) and there's no side covers (or need for them). If I ran pods, the entire "under seat triangle" would be empty space. My saddle is the same height but much thinner, and I removed the rear fender (plan a replacement, but it doesn't intrude on that space).

    LOTS of room to play with.
     
  15. paul.hardy

    paul.hardy Member

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    I will make a concerted effort to work out how the get the picks on. As I was just trying to repalce the air box on an almost standard bike I did not spend to much time making it pretty. However I recon if you wanted to, you could make a preety cool looking air intake sytem for a customise bike if you wanted this way.
     
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  16. Todd A Smith

    Todd A Smith New Member

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    Yea I would love to see those pic Paul
     
  17. XJ550H

    XJ550H Well-Known Member Premium Member

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    paul has not been here after sept 2014
     
  18. XJ75082

    XJ75082 Member

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    I'm in the thought process of this custom air box. While attempting to remove the carbs for a cleaning (p.i.t.a.) I figured the stock air box can go in place of pods. Well after reading about issues you guys are having, I'll go the custom route. Well, I ended up breaking an intake bolt. Turns out mine are very corroded.
    Anyhow, being a fabricator welder for 25 plus years. This is what I'm going to start with for shape and dimensions.
    Cardboard & sillycon
    Its cheaper than steel or aluminum for trial and error purposes. Plus a custom air box will allow for easier carb removal.
    My idea for the electronics is to move them right up under the seat where the fuse box is. Relocate the battery more inboard & cross ways from its factory location. Then fab side cover plates out of aluminum.
     
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  19. PavelK313

    PavelK313 Active Member

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    It might be a unique case but I have had absolutely zero issues using pod filter on my bike after getting it jetted and tuned. I was also scared to get rid of the air box but didn’t have a choice due to the luck of space and I am glad I did. Bike performs as good as factory.
     
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  20. XJ550H

    XJ550H Well-Known Member Premium Member

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    bike ,pod brand and jet sizes please . any other mods besides pods? Standard CV carbs?
     

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