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  1. #1
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    Flywheel Lightening - Why?

    I have heard that if you have your flywheel lightened it will increase holeshot and top end by a couple of MPH. I have also heard that it is not worth the expense.

    If a flywheel weighs 20lbs (a guess) and you take 5 off I can't see the difference if a motor is pushing a 30" prop. To me it's like turning the AC on in a big diesel truck - the change would be so miniscual. If I was a racer and was looking for a VERY slight edge it would make sense to me - along the lines of thinning the blades of the prop and blueprinting the hull. As far as the couple of MPH increase on the top end - again I don't see this as you would still be up against the rev limiter - unless you were a racer and had no rev limiter.

    How much would a good holeshot increase? By my logic not very much - as in miniscual.

    The bottom line that I see here is that lightening a flywheel is for racers only and not for most of us here that just want to go faster on limited budgets. Yea it's $300 but a reflash of an ECU is about the same which would yield very tangable results.

    I am in no way trying to undermine vendors that frequent this site and perform flywheel services - Eric Simon comes to mind - and I have heard nothing but good about his work - but I am just trying to get the proper perspective on all the mods one can do to a motor.

  2. #2
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    A light weight flywheel will give you an extremely small advantage on holeshot with a light boat/high hp setup. It will not make it any faster on top end. The main purpose of the light weight flywheel is to reduce the stress on the top bearing at high RPM by reducing the reciprocating mass of the flywheel. By the way, I'm not near as intelligent as that just sounded

  3. #3
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    There should be no "reciprocating mass" on a flywheel. It should be balanced. As should the components connected to it such as the crankshaft and pistons. Crankshafts always have weights built in to balance them against the pistons.

    I have also never heard of a top bearing failing.

  4. #4
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    the flywheel is a rotating mass,pistons and rods are reciprocating.

  5. #5
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    tj,the main reason a flywheel is hard on top main bearings is the gyroscopic energy carried in the spinning flywheel.This spinning motion causes a stabilizing effect,and it takes a great deal of force to tilt the spinning flywheel back and forth,much like moving a handheld grinder side to side,not easy.Now imagine forcing a spinning 20 lb. flywheel instead of a 5 oz. disk...get the picture.All that force must be supported by the top main.Top mains do fail,chris

  6. #6
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    Like I said I'm not near as intelligent as that sounded

  7. #7
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    Also imposes a huge inertia weight which is transmitted back through the crank and driveshaft when the prop is in and out of the water I would suspect...

    Rick
    2006 Gambler 2200DC/2006 250XS

  8. #8
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    I am sure top mains fail but probably at 9000 RPM's. Do they fail at 6000? Probably never.

    Chris - what forces that spinning flywheel side to side or to tilt?

  9. #9
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    Quote Originally Posted by tj309 View Post
    I am sure top mains fail but probably at 9000 RPM's. Do they fail at 6000? Probably never.

    Chris - what forces that spinning flywheel side to side or to tilt?

    I would assume choppy water conditions...

    Rick
    2006 Gambler 2200DC/2006 250XS

  10. #10
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    So to get back to the core of the discussion - will a lightend flywheel give the average guy looking for a SIGNIFICANT upgrade on his average light rig a boost worth $300? I think not. A racer certainly.

    A guy that wants to go faster could probably spend that money on a new prop or a jack plate and get more.

  11. #11
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    I think of it kind of like reeds, a average boater might not notice fiber over steel but someone who races might. An average guy probubly won't brake one but when you turn up the rpm your more likely.
    Chet Olson

  12. #12
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    tj,rick is correct,light flywheels on these motors were borne of offshore racing where the ride goes from rough to violent...samari,if you try our reeds I guarantee you'll notice a difference,chris

  13. #13
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    I went from a light weight flywheel on my Pro 120, 2liter mota(turn'd 97-9900) to a std aluminium 260 flywheel, and seen NUN, ZERO, NUTT'IN az performance wuz concerned!!!!!....This wuz hole shot/et/top end numbers!!!....

    I have found that on STOCK motaz, tha heavy(cast 40 amp) flywheel will turn a few more rpm on top end, over tha 16 amp flex flywheel.....Now, I figger it's kuz ov tha rotating mass helps tha crank keep goin once it's turn'in, but datz juss my opinion...I do however know that tha 40 amp system puts more magnetik pull on tha flywheel, so to over kum this pull, the extra weight haz to help, or it would LOOSE top rpm.....(this iz 6000-7000 range)

    This iz not sientifik conclusionz, juss my observationz on sum ov my "Gotta Know" tess'in....

  14. #14
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    tj.
    I find on the hundreds of Mercury V-6 engines I have built and build 99% of crank breakages occur above the upper middle main bearing ( IMO the FIRST REAL point of crankshaft containment ) The upper bearings on most V-6 are not IMO the first REAL point of crank movement containment. The movement of the flywheel rearward during acceleration and forward under deceleration plays havoc on any of these engines upper bearings. The movement wallows out the parent metal and allows for clearance to be formed at the bearing race and stresses the crank so breakage occurs right below that point ( under flywheel , and at #1 ,#2 crank journal ) I glue ALL my crankshafts in place at saddle and race areas and have stopped most ALL of that movement at the time of assembly but thats a different subject.. IMO A lighter flywheel WILLl lessen the tendency to have the weight in place to stress the crank and end result a crank breakage. As far as performance gains that seems to be a topic of much discussion for and against which I won't enter into. I have my own opinions about performance gains but the advantage of the longevity of the bearing would be enough for me to make a move if the motor were mine and were going to turn big RPM numbers just as fiber reeds as they have proven to be an insurance policy for longevity...I'd go out on a limb as say most everyone at an outboard drag race event use them, now either they work or there are a bunch of folks that waste a ton of money on bling...

    My .02
    Jay
    Jay @ JSRE


  15. #15
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    [QUOTE][as performance gains that seems to be a topic of much discussion for and against which I won't enter into. /QUOTE]

    Awe Kumm-on.........We ain't butt'd hedz in a while

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