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    Re: Predator 13 hp engines
    #11
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    Herman
    The belts on my wifes I think we just got a cheap belt last time around so I just ordered Kevlar comet belts, cost about double. going with a little lower gearing or 20" tires would help on belt life , just depends on what top speed your looking for, this one tops out about 40, kind of a happy medium. I found that running a 10 tooth on the front I would get a lot more vibrations and howling at certain higher RPM's with the #40 chain. on the spider kart that I did we went with a 10 and 60 tooth, 20" tires but the throttle was limited to about half so it worked out good.
    Big difference between the 780 and the 40 series, the 40 has a 1:1 high and 2.43:1 low where the 780 has .69:1 high and 3.71:1 low. I double checked and mine is running 6.8:1 ratio so I get 25.228:1 low and 4.69:1 high, Wifes gets 14.58:1 low and 6:1 high. Not sure about the HP rating on the 780 some places advertise it at 16 HP and others I have seen as high as 22. Size wise the 780 is a lot bigger so you need a little more room for it. I haven't had to do any fine tuning with weights or springs it just worked out of the box , just gearing started with 6:1 but it bogged a bit in high. They do make a few different driven's for the 780 a 770,780,790 just depends on if you want higher or lower gearing
    Tom
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    Re: Predator 13 hp engines
    #12
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    Taz
    Thanks for taking the time to post details like the ratios.
    It seems clear to me the advantage of using the 780 series is the wide gearing available from 3.71 to .69 overdrive vs the 2.43 of the 40 series.
    This allows for less reduction needed in the sprockets, therefore a smaller diameter sprocket on the axle where ground clearance is an issue.
    So is Comet really out of business to get the Duster or 780 series?
    Seems like the Baja SAE guys are sourcing this stuff and I assume it is not used.
    Thanks again
    Herman
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    Re: Predator 13 hp engines
    #13
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    From what I understand comet went out of business but another outfit bought or took it over. The 780 is still available from quite a few places , I bought mine from
    Search
    If you have room run a little longer belt and CD , I went with the 9.05" CD #300625 belt but when the belt is cold it is stiff and causes a little drag, after it warms up a minute or two it's fine
    Tom
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    Re: Predator 13 hp engines
    #14
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    I am committed to a build.(For kids 6-10 years old, will not fit adults)
    I purchased the Polaris Predator front suspension and coilovers.
    Also the wheels and tires, Kids suspension seat, rear axle, bearings and wheel flanges.
    I ordered a 13HP Predator today.
    Dain254 build was the motivating factor so it is all his fault.

    Now for the CVT decision.

    I am considering Comet 780 series like Taz used which gives the widest shifting ratio (approx. 3.71 to .69) I have seen for around $530. (driver,driven and belt).
    The driven is also 9.05" in diameter which creates a "keep the driven out of the dirt" issue on Dain's rear suspension design which I want to copy.
    The Comet 40 series sells for about $300 at BMIkarts.com .
    BMI has a no name 40 series CVT system for around $150.
    I believe Dain is using the no name BMI CVT with success.
    The 40 series drivens are 7.5" in diameter.

    I would appreciate any feedback on the quality/longevity of the BMI no name 40 series CVT parts before I make a decision.
    Thanks
    Herman
    Last edited by herman pahls; 01-07-2016 at 02:11 AM.
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    Re: Predator 13 hp engines
    #15
    The Bob Ross of MBN Bullnerd's Avatar
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    "Dain254 build was the motivating factor so it is all his fault." LOL!
    "Speed is time-time is speed"-Dennis Hopper

    Quote Originally Posted by TALON View Post
    did you use a special bigfoot camera or something ,you know all blurry could be a tree stump kinda thing .
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    Re: Predator 13 hp engines
    #16
    Protodie Master and Vendor ProtoDie's Avatar
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    Herman,
    we tried 40 series clutches years ago on 6.5 motors in the MXT kids cars
    they worked,,,ok,,, but over 3600 rpms they would shred belts in no time.
    they would not last an hour at 5000 rpms
    could be the belts we were using,,,,I do not remember,,, what ever belt they sent with the package we bought

    We use CV-tech clutches and they work great.
    a lot of SAE baja teams use these too

    I listed specs on these in another thread

    CV-Tech Clutches
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    Re: Predator 13 hp engines
    #17
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    Protodie
    I thought it was the 30 series you had belt problems with ?
    I'm still debating on what system to use on my dual 6.5's , really be pushing the 30 series and the 40 series driver is 1" bore , did find a 44 magnum driver in 3/4" bore with 18 hp 8500 rpm rating.

    Herman
    I have bought and used a few of the china 40 series, on one driven I had to file the bore to fit the shaft and one driver after about 15 to 20 hours use gets sticky and I have to take it apart clean and lube and then it's fine again. other than than that they work and I think the last set I bought on ebay for about $100.
    For a kids only buggy I think the 40 series would be good enough, your'e probably going to want to limit there top speed anyway
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    Re: Predator 13 hp engines
    #18
    Protodie Master and Vendor ProtoDie's Avatar
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    Quote Originally Posted by tazmannusa View Post
    Protodie
    I thought it was the 30 series you had belt problems with ?
    I'm still debating on what system to use on my dual 6.5's , really be pushing the 30 series and the 40 series driver is 1" bore , did find a 44 magnum driver in 3/4" bore with 18 hp 8500 rpm rating.

    Herman
    I have bought and used a few of the china 40 series, on one driven I had to file the bore to fit the shaft and one driver after about 15 to 20 hours use gets sticky and I have to take it apart clean and lube and then it's fine again. other than than that they work and I think the last set I bought on ebay for about $100.
    For a kids only buggy I think the 40 series would be good enough, your'e probably going to want to limit there top speed anyway



    Taz
    I had to go look at the obsolete parts shelf,,,,,,brr its cold over on that side
    but I found a bunch of stuff I forgot I had lol

    you are right though, it was 30 series not 40 we were blowing up
    30 series is 3/4 wide belt and 40 series 7/8 wide belt

    my bad

    so I can't really say on the 40 series clutches
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    Re: Predator 13 hp engines
    #19
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    I have a CVtech sitting around - but my 40 series comet knockoff has been working great with the predator (40 drive and 44D driven - 44D is 1" bigger on the OD giving a higher CVT reduction. I'm guessing the cheap 40 driven that is 7.5" would work just fine though). I will likely make use of the CVtech when I build my 22hp version
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    Re: Predator 13 hp engines
    #20
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    Bullnerd
    This is America, somebody else is to be blamed for my actions.
    I got bit by a clean, fairly simple build by a former SAE Baja member that also incorporates the front suspension and plastic off of Quads.
    I like the way he utilized the rear steer from the Quad upright without messing with the geometry trying to switch to front steer.

    Jody
    Thanks for listing the Specs. on the CVtech CVT's.
    When I read your SS630R build I was surprised by your low geared 13:1 box to get 45 MPH.
    The .45 overdrive of the CVtech explains the math.
    The CVtech prices are right in line with the Comet 780 series.
    Does CVtech offer a combination with 1:1 or very little overdrive?
    I am trying to copy Dain's rear suspension with 20" tires and 5:1 reduction on the sprockets to keep the rear sprocket as far away from the sand as possible and top out at ~40mph at 3600 rpm.

    Dain
    Thanks for letting me know that you are using the bigger diameter 44D Driven for lower gearing.
    Do you have any clue what the high end ratio of your combination is? 1:1 ?
    Thanks everyone for you responses.
    Herman
    Last edited by herman pahls; 01-07-2016 at 01:57 PM.
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