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  1. #1
    PWCToday Guru E350's Avatar
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    What are the Benefits and Detriments to Lightening a 61x Superjet Flywheel ?

    I am removing the flywheel to get a look at the charge, pulser and lighting coils on our 1994 701cc (engine type 61x) square nose Superjet.

    It has been suggested that I send the flywheel out to be lightened.

    What are the benefits of lightening a 61x flywheel, if any?

    What are the detriments to lightening a 61x flywheel, if any?

    I ask because benefits and detriments usually accompany any modification.

    Also from my reading, apparently in the later version of the 701cc (engine type 62T) Yamaha actually increased the weight of the flywheel. If Yamaha decided to make the flywheel heavier in the later version of the 701cc, why would we want to make the flywheel in the earlier version of the 701cc even lighter?
    Last edited by E350; 10-03-2017 at 11:42 PM.
    Learning Slowly...

  2. #2
    PWCToday.com Is My Home Away From Home TMali's Avatar
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    Re: What are the Benefits and Detriments to Lightening a 61x Superjet Flywheel ?

    Pro - Quicker revs and less stress on the crank

    Con - Engine slows down quicker (con for racing mostly) and more stress on the thinner material of the flywheel (can crack and break)

  3. #3
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    Re: What are the Benefits and Detriments to Lightening a 61x Superjet Flywheel ?

    I don't think your'll notice anything much. It's suppose to help with bottom end torque.
    I know you like to read, so here's some old info for you.
    The Group K flywheel comments is there, you just go down the list of engine mod comments.
    http://www.x-h2o.com/index.php?threa...ywheel.113764/
    http://http://www.groupk.com/y633-781sj-all.htm

  4. #4
    PWCToday Guru E350's Avatar
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    Re: What are the Benefits and Detriments to Lightening a 61x Superjet Flywheel ?

    fx1dave: Yup, I like to read. Learning to see is the biggest part of any new endeavor for me. Some people can just look at something and say "I bet that thing does ____" or "That's not right." But I know how I learn and I don't always see what is in front of me unless I know what to look for. And the quickest path for me to learn what to look for is by reading.

    So a great big thanks to you fx1dave and to the others on this forum (and on the x).

    For those who don't like to read as much as me, here are a few salient excerpts from the x link fx1dave provided (I couldn't open the groupk link):

    ThatGuy said: "any truth to it being easier on your crank?"
    Vumad said: "The flywheel dampens vibration. Lightening the flywheel is harder on your crank in theory. It's for more power, not for more reliability.

    Matt_E said: - "a lighter flywheel will very noticeably decrease the motors ability to sustain power at any given RPM. Go through chop with a TL system and you'll see what I mean. The RPM's climb to the moon when the pump leaves the water and drops back down instantly when it re-enters the water. Have a ski with stock flywheel and let off the throttle and then do the same with a ski equipped with lightweight flywheel or TL - the TL ski slows down rapidly. The stock flywheel ski will keep going for quite a while.
    Having TL is great for power and rev-up, but it also revs down very fast - kind of like having brakes.

    That added angular acceleration and deceleration is harder on the crank, not easier.

    A flywheel is just a big mechanical energy storage device, kind of like a capacitor for your motor. It absorbs a bit of power from the motor and thus takes longer to spin it up. But, that energy is available for the motor to use when there isn't enough energy from the combustion process.


    Vumad said: "A lightweight flywheel can be had for $50 (#Zero) and keep your motor reliable. It will improve your bottom end to a minor amount, but might hurt the top some, all while adding a little extra wear on your crank. If you want hit off the bottom, like most people here do, then it's probably right for you, but if you are racing, on a tight budget, or want the absolute max reliability, it may not be the best thing for you.

    Everything is a trade off. Money, power, reliability, noise, ease of handling. You have to make the choice of how much of which you are willing to sacrifice to gain how much of which."
    Learning Slowly...

  5. #5
    PWCToday.com Is My Home Away From Home spitz15's Avatar
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    Re: What are the Benefits and Detriments to Lightening a 61x Superjet Flywheel ?

    Couldnt disagree more. I did the same thing that you are asking about last year to one of our 94 superjets and a blaster as well. It was a very noticeable gain over the stock flywheel. Now every ski i own gets a lightened flywheel.
    Im addicted...

  6. #6
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    Re: What are the Benefits and Detriments to Lightening a 61x Superjet Flywheel ?

    Here's a new link. Zero does nice work and it's not a reliability issue.
    This is basic Issac Newton's laws of physics.
    http://www.x-h2o.com/index.php?threa...ywheels.37809/

    http://www.groupk.com/superjet.html

  7. #7
    Top Dog Benflynn's Avatar
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    Re: What are the Benefits and Detriments to Lightening a 61x Superjet Flywheel ?

    Sometimes we put flywheel weights on trail bikes, heavier flywheel will knock the hit out of and broaden the powerband, lighter makes traction more difficult, i imagine a lighten flywheel will cavitating more readily due to lower mass

  8. #8
    PWCToday Guru E350's Avatar
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    Re: What are the Benefits and Detriments to Lightening a 61x Superjet Flywheel ?

    From the GroupK article linked above:

    "Ignition Flywheels – All Super Jets use the same stock steel ignition flywheel. As a percentage of the total rotating mass of the crankshaft, this flywheel is relatively small. Despite that, quicker throttle response can be had by reducing the flywheel’s weight. There are many shops that lighten the stock flywheels (Group K included). We have experimented with many different lightening modification levels on these flywheels. It is possible to lighten the stock flywheel by as much as 1.5 pounds. However our testing showed that when the stock flywheel is lightened by this margin, there is a very high risk of fracturing, and eventual flywheel disintegration (a very destructive failure). The lightening modification that we found to have no long-term reliability weaknesses reduces total weight by .4 pounds. While this is not a big reduction in total weight, we remove this weight near the outer perimeter of the flywheel (where it has the greatest effect on total inertia). The end result is a very noticeable increase in throttle response and acceleration, as well as no compromise in long term flywheel life (note: IJSBA only permits this mod in freestyle and Super Stock classes).

    Lightweight aluminum "charging" flywheels (to replace the stock steel unit) have become common in the aftermarket. These lightweight flywheels (legal for use in freestyle and Superstock) can offer big reductions in rotating mass, that generate big increases in engine acceleration rate. While many racers have used these flywheels successfully, they can cause a "side effect" problem in a stand up application.

    Most racers interested in a super-light aluminum ignition flywheel, for a Super Jet, are Super Stock class racers. Most of these racers are running big bore top ends in the 771cc-781cc range. These large displacement top ends generate so much sheer horsepower that they can make a stand up machine very difficult to control, and even more difficult to keep hooked up. The increased engine acceleration from an aluminum flywheel (on a stand up) further complicates these problems. We have seen many instances where riders installed the lighter flywheel, and then cut slower laps as a result of increased difficulty keeping the pump hooked up. Some of this "hook up" problem can be resolved by installing a stainless steel Skat Trak pump assembly. The rest of the hook-up difficulties are left up to the rider.

    Our basic recommendation for any non-pro racer (using a stock pump case) is to lighten the stock ignition flywheel. For pro racers that will be using the Skat Trak pump, get the aluminum flywheel … and eat your Wheaties (you’ll need ‘em).

    Total Loss Ignitions – It has been popular for so top level pro racers to fit an aftermarket "total loss" ignition. The term total loss means that there is no charging system at all. The battery provides all the voltage needed to make sparks … and that energy is totally lost (instead of being replaced by a charging system). The lightweight flywheels of total loss ignitions can offer a huge increase in engine acceleration (for those that can handle it).

    We have experienced "random" reliability with total loss ignitions to such an extent, that we will not fit them to any of our engine packages. If you choose to use a total loss ignition unit, be sure that you have a contact person at the purchase point that can help you with technical and/or diagnostic issues."


    http://www.groupk.com/superjet.html

    If I were to try a lightened flywheel, I think I would buy an aluminum flywheel from #zero and keep my stock flywheel to put back on if I wanted to go back to stock:

    http://www.x-h2o.com/index.php?threa...ywheels.37809/
    Learning Slowly...

  9. #9
    PWCToday.com Is My Home Away From Home
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    Re: What are the Benefits and Detriments to Lightening a 61x Superjet Flywheel ?

    No one makes a new Aluminum wheel for a 61x. Chances of finding a good one are very slim.

  10. #10
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    Re: What are the Benefits and Detriments to Lightening a 61x Superjet Flywheel ?

    I believe Jet netics makes one?
    triceps are the biceps of the back of your arm.

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