Benifits of Stroker Crank?
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  1. #1
    I dream skis FreestyleRiverRat's Avatar
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    Benifits of Stroker Crank?

    Hello everyone,

    I am throwing around ideas for my 701 swap in my 650 SJ. I am going with a 61x with freestyle ported cylinders running my current DG performance 38's, a factory b-pipe with mod chamber and head with pump gas domes. My question is about the crank. I picked up some clearanced and ported 61x cases, what benifits would I see from switching from the stock crank to a stroker crank. Is it worth the $$ and will it sacrafice reliablity. I remember reading an old article from Group K where they did tests and did not see any significant increses in performance over a properly modded motor like there Hammer kits.

  2. #2
    PWCToday.com Is My Home Away From Home Waxhead's Avatar
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    the stroker crank makes more torque
    as the big end pin is further out from the centre
    Www.waxracingproducts.com
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  3. #3
    PWCToday.com Is My Home Away From Home SuperJETT's Avatar
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    One thing to remember about Group K is that they are in business to make money, so they will normally portray their mods in a better light then others. Most of the info Harry puts out is great info though.

    Here's a good article from a different perspective that specifically talks about 650/701's.
    http://www.hpt-sport.com/stroknot.htm

  4. #4
    PWCToday.com Is My Home Away From Home mile9c1's Avatar
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    Group-K's big knock on the strokers is that they weren't any faster than the big bores (though they wear out faster and they are more expensive to build).

    You'll need different cylinder porting with a stroker crank, so keep that in mind if you already have a ported cylinder.

    I read somewhere that they vibrate more (because of the rod length/stroke ratio) but I can't really tell (I have a 5mm stroker with an Able cylinder).

  5. #5
    PWCToday.com Is My Home Away From Home mile9c1's Avatar
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    Quote Originally Posted by SuperJETT
    Here's a good article from a different perspective that specifically talks about 650/701's.
    http://www.hpt-sport.com/stroknot.htm
    I must have missed something... his program estimated 50 horsepower for a stock 701? Which formulas are he talking about?? Why does he start off by saying the Kawasaki 650 engine makes better power than the 701??

    I think he knows a lot about engines but he needs to rewrite that article; the Group-K articles are much easier to follow. It sounds like he likes strokers, but he didn't address the piston-speed issues that GroupK does, nor real life test results. Even his program generated horsepower numbers are vague.

  6. #6
    PWCToday.com Is My Home Away From Home Waxhead's Avatar
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    he is using the tsr software
    to get his figures

    the stoker crank has a higher piston speed but if you use the long rod crank it drops the max piston speed right down
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    PWCToday.com Is My Home Away From Home mile9c1's Avatar
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    Quote Originally Posted by jetski_waxhead_au
    the stoker crank has a higher piston speed but if you use the long rod crank it drops the max piston speed right down
    Does anyone make a long rod 5mm stroker crank?

    The problem with a long rod (I think this is what GroupK claims) is that by moving the piston up you lose cranking compression in your bottom end.

  8. #8
    PWCToday.com Is My Home Away From Home Waxhead's Avatar
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    i am sure they wouldnt be so silly to say that
    when with moden pipes and the scavenging we get that we try and create more room in the crankcases

    stuffed crankcases make for short power bands

    they used to do that in the old days
    i think they still do it on weed whackers but they dont have decent tuned pipes
    Www.waxracingproducts.com
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  9. #9
    PWCToday.com Is My Home Away From Home SuperJETT's Avatar
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    George probably wrote that article back in '94, things have changed a lot but with his medical condition and being retired, I seriously doubt he would bother to update anything.

  10. #10
    Resident Guru freestylegeek's Avatar
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    If you're going stroker, you might as well do it right.
    Those 61X cases and a 61x cylinder aren't going to give you the the output that you could get with 62t cases and a Lamey cylinder. BUT, that's big money.
    Quite frankly, you can build a nice motor with what you've got, there's plenty of little tips and tricks on here to get your 61xcase/61xcylinder motor in the 90-100hp range.

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