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Thread: DIY dyno

  1. #16
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    Quote Originally Posted by FastFred View Post
    CVT, very interesting. The dyno curves are different to what I am used to seeing with geared bikes. Can you tell me what to look for in a CVT dyno curve.
    I neither could learn something from that powergrahp

    I first did the engine with the CVT blocked to get the ignition right (like the graph a few psts before), tested 3 pipes but as I already thought, the one we used before was the best.

    than it's setting up the CVT and clutch, and for that I don't use the power graph but only the time/speed table : the faster you get to your top speed, the better the setup is

  2. #17
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    Thanks, I asked because CVT is not that common in racing here, so very few have much experience with it but it looks very interesting.
    Factual Facts are based on real Fact and Universal Truths. Alternative Facts by definition are not based on Truth.

  3. #18
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    Hmmmm, CVT transmission would kinda make its own dyno graph. The horse power number isn't relevant at all, just the wheel speed after a set length of time.

    That's great for tuning if you graph the speed like is done here. Brilliant.

    Edit. Oh, I see this was said in the next page already.

  4. #19
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    Quote Originally Posted by JanBros View Post
    I neither could learn something from that powergrahp
    thnking again about it, a good graph needs to look like a steady decline in power just like the one on top.

    if for example the CVT would open too soon, you will see a sudden rise in power because the CVT will be full open before rpm of max power, so that by the time that rpm is reached, the power will also increase.

    if the CVT is setup correct, it should only start to open (change gearing) at max power, and from then on keep the rev's at max power while continualy opening further.
    as a result, the actual power of the engine stays the same, but the wheel/roller rpm drops. so the software will see this as a drop in power.

    than again, if the CVT starts to open too late (after rpm max BHP), you might not know this from looking at the graph because the graph will show a drop in power anyway. so you'de always have too start with a CVT that opens too soon first, if you do not Dyno the engine first with a blocked CVT.

  5. #20
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    Thank you for the explanation, CVT is something we are interested in trying, but first we have to understand it.
    Factual Facts are based on real Fact and Universal Truths. Alternative Facts by definition are not based on Truth.

  6. #21
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    Quote Originally Posted by FastFred View Post
    Thank you for the explanation, CVT is something we are interested in trying, but first we have to understand it.

    below is an answer from Frits to a question of me regarding a CVT set-up problem on Pit-Lane.biz. My problem was that from standing still everything worked perfect, but when I re-opend the throttle at low speeds (just before the clutch would release itself) after some runs up and down the street, the engine wouldn't pick up. It seemed as if the clutch gripped sooner because of heating up or something like that.

    his anwser was a good explanation of how the secondary sheaves, spring and slots work together :

    The slots in the secondary pulley serve to support the working of the secondary spring. The more torque that is being transmitted trough the slots, the more the secondary pulley sheaves are pushed together.
    If you close the throttle, the torque diminishes and the secondary sheaves can move wider apart. The drive-belt will ride lower in the secondary pulley and higher in the primary pulley on the crankshaft. Engine rpm goes down, exactly what the ordinary customer expects when he closes the throttle.
    For racing you want the engine rpm to be constantly at the value for maximum power. You can help this by applying axial slots. But axial slots will not support the working of the secondary spring at all, so you will need a heavier secondary spring in combination with those axial slots.


    picture :

  7. #22
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    I built this a few months ago and thought some of you blokes might be interested. The dyno is extremely simple, primitive even. But it works very well, is accurate and repeatable. The only downside is that it doesn't give a direct hp reading, you have to work it out from the rpms and torque reading. I have a spreadsheet set up so that all I have to do is punch those two numbers in and it spits out the hp figure, corrected for current weather conditions.

    The absorbing element is a bloody big ventilated disc brake, 380mm and 15kg, so it's bigger than a Chev flywheel and twice as heavy. It's mounted on a hub that spins on needle bearings around the spindle. The caliper is free to rotate around the spindle too, and is only restrained by a torque arm exactly 12" long that is connected via a cable to the torque gauge. This gauge is just a dial type spring scale, just like those of the older mechanical dynos. If you wanted to get fancy a load cell would work just as well.

    I used this style instead of an inertia style because I wanted to be able to run at full load for an extended period, something an inertia dyno can't do. I need to know that the engine is going to survive an extended full throttle run without seizing or holing the piston.I also didn't want to deal with the inconsistencies that go with a tyre on a roller. The absorbed energy is converted to heat, just like any other dyno. With short runs - say 10 seconds or so - I don't even have to run a blower on the brake, I just let it spin a bit in top gear and the natural circulation of air through the disc is enough. For longer runs and higher power levels I direct an air blower into the "inside" of the disc, and this allows it to run loaded indefinitely. But for normal tuning work, by the time I've changed the jets or timing or whatever it's good to go again. It's never been hot enough to even turn bluish yet, though it's only had to deal with around 55hp. The only thing I might do is put a shroud around the brake so I can direct the hot air outside where it won't affect the engine output. Because of the bikes overall gear ratio the rear hub never sees more than about 2000rpms so I don't have to worry about it bursting. You certainly wouldn't want to try running the iron disc at anything approaching engine speeds though...

    But like I said, it works very well, cost under 2k and took a couple of half-arsed weekends to build.






  8. #23
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    Looks really good. ....
    Factual Facts are based on real Fact and Universal Truths. Alternative Facts by definition are not based on Truth.

  9. #24
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    Quote Originally Posted by JanBros View Post
    below is an answer from Frits to a question of me regarding a CVT set-up problem on Pit-Lane.biz.

    picture :
    Thank you for the picture and explanation.
    Factual Facts are based on real Fact and Universal Truths. Alternative Facts by definition are not based on Truth.

  10. #25
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    i will be picking your brains re a race CVT, you have been warned


    The slots in the secondary pulley serve to support the working of the secondary spring. The more torque that is being transmitted trough the slots, the more the secondary pulley sheaves are pushed together.
    If you close the throttle, the torque diminishes and the secondary sheaves can move wider apart. The drive-belt will ride lower in the secondary pulley and higher in the primary pulley on the crankshaft. Engine rpm goes down, exactly what the ordinary customer expects when he closes the throttle.
    For racing you want the engine rpm to be constantly at the value for maximum power. You can help this by applying axial slots. But axial slots will not support the working of the secondary spring at all, so you will need a heavier secondary spring in combination with those axial slots.

  11. #26
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    there are some good post from around these pages
    http://www.kiwibiker.co.nz/forums/sh...post1130438278



    Kinky is using a feather. Perverted is using the whole chicken

  12. #27
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    16th November 2005 - 07:48
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    Here we go Dyno geeks. Just popped up on my on of the buy/sell groups I follow on FB. Set up for karts but thought it was cool.



    http://www.ebay.com/itm/272435674993...84.m1555.l2649

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  13. #28
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    Quote Originally Posted by Pumba View Post
    Here we go Dyno geeks. Just popped up on my on of the buy/sell groups I follow on FB. Set up for karts but thought it was cool.



    http://www.ebay.com/itm/272435674993...84.m1555.l2649
    Ouch... not cheap...

  14. #29
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    Quote Originally Posted by Bert View Post
    Ouch... not cheap...
    Haha, never said it was. Quality bit of kit though.


    Sent from my iPhone using Tapatalk

    For the record Qkkid was in my bed, not the other way round

    Quote Originally Posted by Yow Ling View Post
    Pumba is a wise man.

  15. #30
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    Kinky is using a feather. Perverted is using the whole chicken

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