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    TAV-2 Driven Pulley Tuning

    Anybody try tuning the 30 series Driven Pulley for drag racing a minibike?

    Either switching from the middle preset hole, or swapping to the stiffer "Yellow" Spring?


    I'm putting a built Predator on an El Lobo minibike with a 30 series TC.

    Going to try the 6" Pulley first and see how it does.

    ~13" Tires
    54T Rear : 10T TC

    4000 RPM Driver Unit Engagement.
    Looking for ~7000-7500 Max RPM

    Lets say I'm trying to tune the TC Driven for fastest 1/8 mile time... Anybody ever play around with that? I've got the stock spring and the yellow spring. I've only used the stock spring in the middle hole, but have always wanted to test this out.

    I was thinking the Yellow spring would put more torque to the wheels for fastest acceleration, but not really sure how delaying the up-shift would change drag times.

    I'm guessing it depends on the powerband of each engine, but wondering if anybody toyed around with this and recorded any findings. Or if anybody has any theories.

  2. #2
    Senior Member TheDullCarbide's Avatar
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    Quote Originally Posted by bob58o View Post
    Anybody try tuning the 30 series Driven Pulley for drag racing a minibike?

    Either switching from the middle preset hole, or swapping to the stiffer "Yellow" Spring?


    I'm putting a built Predator on an El Lobo minibike with a 30 series TC.

    Going to try the 6" Pulley first and see how it does.

    ~13" Tires
    54T Rear : 10T TC

    4000 RPM Driver Unit Engagement.
    Looking for ~7000-7500 Max RPM

    Lets say I'm trying to tune the TC Driven for fastest 1/8 mile time... Anybody ever play around with that? I've got the stock spring and the yellow spring. I've only used the stock spring in the middle hole, but have always wanted to test this out.

    I was thinking the Yellow spring would put more torque to the wheels for fastest acceleration, but not really sure how delaying the up-shift would change drag times.

    I'm guessing it depends on the powerband of each engine, but wondering if anybody toyed around with this and recorded any findings. Or if anybody has any theories.
    Using the third hole with a green spring gives a lower rpm than a yellow in the second. You should tune the garter springs before the contra because the garters affect both engagement AND acceleration rpm.

    The yellow spring (or green in the third hole...anything that increases tension) increases torque because with high HP engines, the belt can slip down into the driven at a hard engagement. A harder spring reduces this because it keeps the driven halves tighter on the belt. The 7" driven can also help because it has more surface area for the belt to grip on at engagement. The trade-off of the 7" is that it has less shifting range than the 6".

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  4. #3
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    I don't know jack but would bet that the 7" would work better for drag racing. Don't you want the highest RPM's possible at the end of the 1/8th? If you tried both with identical gearing you would have higher RPM's at the end of the run with the 7".

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    Quote Originally Posted by SAS289 View Post
    I don't know jack but would bet that the 7" would work better for drag racing. Don't you want the highest RPM's possible at the end of the 1/8th? If you tried both with identical gearing you would have higher RPM's at the end of the run with the 7".
    54:10 with 6" pulley is 4.86 :1 in highest "gear"
    54:10 with 7" pulley is 6.05 :1 in highest "gear"

    So yes the 7" pulley will rev faster and get to top speed quicker
    7500 RPM is 46 mph.

    With the 6" pulley
    6000 PRM is 46 mph
    7500 RPM is 57mph.

    I think you want the fastest speed at the end of the run, not necessarily the highest rpms.
    But I don't really know, that's why I am asking.

    The engine will run out of power, or the cam will run out of air, at some RPM.
    I don't think many people are using the NR285-0211 Cam on a minibike with TC. So not much to go off of.
    Approx .285 lift and 250 duration (at .050).Best with 24 mm Mikuni, big valves, and high compression.
    7000 RPM. 11.0 to 1 compression or more. 26+ lb Springs Required, Small track cam for serious torque


    There's not much info out there about tuning the secondary pulley except one hole for flat riding, one hole for medium, one hole for hilly, yellow spring for more torque.

    I just ordered the minibike. I don't know how long it will take. I got it powder coated.

    Maybe I'll start a thread when I get it and start testing.
    The engine is built. The TC installed with "White" garter springs, Die Cast Aluminum Weights, Yellow Driven Spring is second hole. Just waiting on the bike now.

    BTW This isn't going to be a "drag" bike, but that doesn't mean I won't want to gear it for drag racing sometimes.
    I think I want to gear it 54:11 with a 6"( or 54:14 with the 7") and see how goes. I should be able to top out at over 60mph and over 7k RPM (not necessarily in an 1/8, but hoping in a 1/4??? . Hoping a long stretch and I can get up to 7500 RPM with that gearing. But sometimes I just want to wheelie, so I might throw an 8T on the Jackshaft.
    Last edited by bob58o; 09-15-2017 at 03:30 AM.

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    Yeah. I think better stated would be to gear for the RPM with the most power to be seen at the end of the run. Not the most RPM.

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    Quote Originally Posted by bob58o View Post


    I don't think many people are using the NR285-0211 Cam on a minibike with TC. So not much to go off of.
    Approx .285 lift and 250 duration (at .050).Best with 24 mm Mikuni, big valves, and high compression.
    7000 RPM. 11.0 to 1 compression or more. 26+ lb Springs Required, Small track cam for serious torque

    .
    Keep us posted on this. I am going to baseline my bike with more or less a stock Hemi, then tear down this winter and do a mild build. I know it will be slow, but I'm and engineer and like before/after results...haha

    I want to stick with the TAV, but I have been struggling with cam selection... I don't want to spin it to the moon...

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    bob58o, i did some testing earlier this year with a yellow spring on my drag bike that was setup for 125ft on clay. was not happy with the results. running a stiffer spring in the driven on my bike just seam to create Havoc with the belt. engine was a built tecumseh ohv motor. never had it dyno, it was running a 22mm mikuni/clone carb with a 140jet and turning close to 8000 rpm's.
    when the belt had to go through it's motions and using the stiff spring it was like locking up the rear pulley and the belt still wanted to travel down but it couldn't and at that point it just was slipping. now all of this was mounted on a fix area with minimum adjustment(non-adjustable) now maybe if you can adjust your belt tension the problem might go away?
    another problem i encountered with the driver was the stall springs. you will have install a higher stall springs if you want the bike to come out of the hole faster and i don't like the way comet stall works at all. i installed a set of 3000 stall springs(was not enough for my bike). the problem i got was the springs wanted to engage at a lower rpm and that varied after the unit got hot and the unit would also create some unwanted vibrations. so thats telling me the unit does not want to balance very well? i verified this with couple different motors.
    let us know when you test your drive train out. i like to see what kind of results you get. each bike build varys,so your results may be better or worst or the same?
    goodluck....

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  11. #8
    Senior Member TheDullCarbide's Avatar
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    Quote Originally Posted by delray View Post
    bob58o, i did some testing earlier this year with a yellow spring on my drag bike that was setup for 125ft on clay. was not happy with the results. running a stiffer spring in the driven on my bike just seam to create Havoc with the belt. engine was a built tecumseh ohv motor. never had it dyno, it was running a 22mm mikuni/clone carb with a 140jet and turning close to 8000 rpm's.
    when the belt had to go through it's motions and using the stiff spring it was like locking up the rear pulley and the belt still wanted to travel down but it couldn't and at that point it just was slipping. now all of this was mounted on a fix area with minimum adjustment(non-adjustable) now maybe if you can adjust your belt tension the problem might go away?
    another problem i encountered with the driver was the stall springs. you will have install a higher stall springs if you want the bike to come out of the hole faster and i don't like the way comet stall works at all. i installed a set of 3000 stall springs(was not enough for my bike). the problem i got was the springs wanted to engage at a lower rpm and that varied after the unit got hot and the unit would also create some unwanted vibrations. so thats telling me the unit does not want to balance very well? i verified this with couple different motors.
    let us know when you test your drive train out. i like to see what kind of results you get. each bike build varys,so your results may be better or worst or the same?
    goodluck....
    What driven do you run? I had some similar slippage issues with the 6". If it's not that, maybe the belt is getting hot and glazing at such high rpm? As for the driver being unbalanced, it's kinda hard for Comet to balance a sheave spinning 8000rpm that rides on 3/8" of crankshaft but hangs off another 3/4". I machined a little shaft extension sorta thing to replace the bolt on the end of the PTO. It works alot better than the previous setup...a bolt with about 6 washers.

  12. #9
    delray's Avatar
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    when i was doing the testing early this summer i was using a 7" 30 series with a new belt. all this was done with a fix mount setup(comet steel mounting plate). i was lucky on the crankshaft. i was using a 3inch shaft. for the unwanted vibration i was getting it at about 2000 rpm's . right about where my built motor would idle. this made it little bit harder to adjust the carb and you could still feel it little bit in the higher rpm's too. on a stock engine you really don't feel anything when the bike idle's at 1000rpm's or so. my opinion i think the yellow spring would work better with a stock/low horse engine where the acceleration and speed is much slower and the belt has a chance to grip the pulley and make everything go through it's motions. when a engine is turning some crazy amount of rpm's i just don't see how the belt could work proper and using one side of the belt to grab (30 series design) just doesn't work for me.
    i have found under racing condition it is better to just let the driven go through it's motions.
    Now for just racing condition only. i don't even waste my time with a 30series. for fun and on a mild bike it works great still.
    right now i am setting up a off-road minibike(thunderbolt) with a 7 inch 30 series and also modifying the stock comet plastic torque converter cover so it will fit over all of it and stilll make the cover look stock......
    Last edited by delray; 09-16-2017 at 10:57 PM.

  13. #10
    Senior Member TheDullCarbide's Avatar
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    Quote Originally Posted by delray View Post
    when i was doing the testing early this summer i was using a 7" 30 series with a new belt. all this was done with a fix mount setup(comet steel mounting plate). i was lucky on the crankshaft. i was using a 3inch shaft. for the unwanted vibration i was getting it at about 2000 rpm's . right about where my built motor would idle. this made it little bit harder to adjust the carb and you could still feel it little bit in the higher rpm's too. on a stock engine you really don't feel anything when the bike idle's at 1000rpm's or so. my opinion i think the yellow spring would work better with a stock/low horse engine where the acceleration and speed is much slower and the belt has a chance to grip the pulley and make everything go through it's motions. when a engine is turning some crazy amount of rpm's i just don't see how the belt could work proper and using one side of the belt to grab (30 series design) just doesn't work for me.
    i have found under racing condition it is better to just let the driven go through it's motions.
    Now for just racing condition only. i don't even waste my time with a 30series. for fun and on a mild bike it works great still.
    right now i am setting up a off-road minibike(thunderbolt) with a 7 inch 30 series and also modifying the stock comet plastic torque converter cover so it will fit over all of it and stilll make the cover look stock......
    I agree the headache of getting a 30 series working just right for drag racing is a waste. There are much better alternatives that will get you there.

    Then again, I'm still with 30s for stock and mild builds.

 

 
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