intake pipe

Discussion in 'Motorized Bicycle General Discussion' started by breno, Aug 19, 2010.

  1. breno

    breno New Member

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    Hi all new to this forum. I have a 70cc skyhawk motor with the expansion chamber and the 36T rear sprocket. I was wondering if there would be any gains to making the intake pipe say 80% of the capacity of the motor. Ive heard there can be gains when do this to cars I was wondering if the same princibal would apply with our bikes. Thanks in advance guys I look forward to your feedback..trk
     
  2. mr.WFO

    mr.WFO New Member

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    opening the intake any larger than the carb throat won't do any good.
     
  3. BarelyAWake

    BarelyAWake New Member

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    You may find this of interest if you've not seen it already: http://motorbicycling.com/f13/bicycle-engine-basic-porting-16646.html

    ...but, anything much beyond that would indeed be pretty much a waste of time as mr.WFO is essentially correct - you're limited by the smallest diameter in the entire system (fuel and exhaust)... though I will say the aluminum intake manifolds are notorious for having too small an inner diameter, having to make up for a lack of strength with a thicker sidewall.
     
  4. breno

    breno New Member

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    Thanks for the replys fellas. Here is a pic of an intake pipe I had to make up.
    Looks like Ive got alot of catching up to do plenty and plenty to read. Cheers Brendan
     

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  5. breno

    breno New Member

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    Here is a pic of my ride. The other photo was when it was on the 66cc. Cant wait to get a XL alloy frame so it all fits together the way they were designed to. Happy modding fellas

    Just saw this smiley it goes well considering I just lost my drivers license.xx.
     

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  6. city of angels

    city of angels New Member

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    wow thats a tight fit
     
  7. breno

    breno New Member

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    yep it took plenty of patience to get it all together, everything had to be bent or manipulated to get it into place and o'yeah wat rear engine mount..lol
     
  8. Andyinchville1

    Andyinchville1 Manufacturer/Dealer

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    HI Breno,

    Just curious but how does he longer runner affect the performance?....I am assuming you are using the same inside diameter tubing as the steel factory intake?

    Thanks!

    Andrew
     
  9. breno

    breno New Member

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    Yeah i am using the same size tube. But my theory is the longer the intake tube the more chance the air has to make a homogenous mixture with the fuel/oil. The more the fuel can be vaporised (in spray form rather than wet) the better the combustion should be. I am thinking this way as I remember seeing the high rise carby setups on the older v8's this was used to increase the volume of the air inlet manifold. I read somewhere along time ago that the ideal setup for a car is to have the inlet manifold approx. 80% of the cylinders capacity. I was just simply trying to apply the same princibals with my motorised bike. Not trying to state any gosbel just throwing an idea out there.
     
  10. GearNut

    GearNut Active Member

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    Well, considering that a 2-stroke engine's intake charge goes into the flywheel cavity before going to the combustion chamber, adding any more length to the intake manifold would be a moot point.

    4-strokes are a whole different beast.
     
  11. breno

    breno New Member

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    touche.. my bad
     
  12. breno

    breno New Member

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    Thought I'd just add a new pic of the recent mod. It looks horn best money spent so far. Only I just got swap back to the standard filter setup when it rains. No big deal though thought about making a cover but that would sought of defeat the purpose imo.
     

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  13. WaterDog

    WaterDog New Member

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    Hows that K&N filter working out for you. That is exactly the style and size i am thinking about for my new build. Any performance difference over the stock filter. Also, do you recall the filter diameter? Is it a 1 inch hole (inside filter hole diameter)?
     
  14. breno

    breno New Member

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    Performance wise it didnt really make any gr8 diference but it sounds alot throatier.
    Yep I got the 25mm filter it cost me $44AUS.
    A few tips on fitting
    *cut the back of the filter out marginally smaller back of the carb to ensure a good seal still
    *Drill 2 4mm holes in line with the existing holes where you bolt the factory one on through the whole filter.
    *try to drill the holes through the V in the filter to slide the longer 4mm bolts u will need through without damaging the filter (i used alan key bolts imo they look betta)
    *Bore out the back of the filter where it attachs to the carb so the choke nut wont clash
    *I drilled a small hole in the bottom where it joins to the carb so the excess fuel can get out
    *After you have bolted it on the fxxker is never going to fall off.
    Personally I chose not to use the other style filter because I wasnt confident it would stay on that good.

    The best mod to do with this little upgrade is to shorten the intake pipe as much as you physically can. I actually also pack welded around the pipe so I could bore the shape of the intake port of the motor as far in as I could before it had to straighten out to slide into the carb (I usd a rubber O-ring to seal er up betta). It is only 30mm long i know but i wanted the best I could do. I actually ended up with something like a welded cast as im pretty sure i dremilled the hole of the 1st half of the pipe out trying to match it up. Also with pack welding it you can virtaully get rid of that angle on the inside of the pipe where it usually kinks down in the standard pipe. If ur interested I can put up a few piccys.

    Good luck, Brendan..
     
  15. breno

    breno New Member

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    heres a pic anyway of the overall.

    if u want any pics of the intake pipe inside and out let me know


    Cheers Brendan
     

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  16. WaterDog

    WaterDog New Member

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    Perfect. Great explanation and thanks for for the pic. That helps a lot.
     
  17. GearNut

    GearNut Active Member

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    The filter looks awesome! You did a good job with the fitment. I really appreciate your detailed mounting instructions, breno.

    Just a word of caution though; a drain hole is not necessary. Any excessive fuel that may accumulate inside the filter will easily flow through the cotton filter media.
    Any extra holes in the filter, filter mount on the carb, ect. will only allow unfiltered air to get sucked into the engine. Even if it is a teeny tiny hole, unfiltered air will still get sucked through it.
     
  18. Nashville Kat

    Nashville Kat Active Member

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    Go with a billet intake from Creative or Pirate- less than $15- I reamed mine a little- FANTASTIC difference in carburetion!

    I also like to drill a couple extra holes in the stock intake filter cover.

    oops- not letting me attach a photo I already posted- when did this happen?

    here's the link to the page then-
    http://motorbicycling.com/f3/upgrades-mods-stock-13886-3.html
     
  19. breno

    breno New Member

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    heres a piccy of mine fitted with the intake. Now when i go full throttle up a hill, etc. it doesnt bog down. Only i have to keep my eye on the plug its borderline being too lean.
     

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