Flywheel Lightening - Why?

[tj309]

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.

[Brian Harden]

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. :cheers: By the way, I'm not near as intelligent as that just sounded:eek:

[tj309]

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.

[ChrisCarsonMarine]

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

[ChrisCarsonMarine]

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

[Brian Harden]

Like I said I'm not near as intelligent as that sounded:thumbsup:

[TheRickster]

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

[tj309]

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?

[TheRickster]

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

[tj309]

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.

[samari]

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.

[ChrisCarsonMarine]

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

[T-REX]

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....

[Jay Smith]

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

[T-REX]

[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:eek::D:D:D

[Jay Smith]

T-Rex my Mom is 88 ( a little younger than you ) and is suffering with the same "demincha and oldhiemers" you have , I've learned now how to deal with YOU folks... The key is knowing their limitations and don't push ya'lls knowledge envelope and attention span level...

:eek::eek::eek::thumbsup::thumbsup::thumbsup:;);););)

Your bud,
Jay

[T-REX]

don't push ya'lls knowledge envelope and attention span level...


Wake up Pee Wee...I don't carry my knowlege in a envelope, an I'z too po ta pay attention.....

But Me an yo MAMA iz twice az tall az U, an U gunna find one day dat OLD IZ GOOD.....keep dem birtdayz kumm'in:D:D

[RB in NM]

Now ya'll quitcher bickerin'...... play nice.....:rolleyes:

I once was told that the lightweight flywheel was first developed for F1 type racers for Deceleration purposes in cornering......wux that a puff ov smoke up my kiester??

RB

[dez nuts]

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.For sure on this statement you would gain 10times more on a normal run around boat by alittle in setup or prop than you ever would in a lightened flywheel by far.On most boats you will see no gain, Your top end will not be any better at all and on a normal run around boat you will not see any holeshot gain that you could notice without a stop watch if you have a 6000 rpm motor you are wasteing your time and money even thinking about lightining your flywheel now maybe if you have a 3litre motor and are trying to spin it up near 7 i would look into this and it will help save your crank shaft. Dave:cheers:

[T-REX]

Now ya'll quitcher bickerin'

We ain't bikker'in...He no'z I reely juss like jerk'in tha Lil Peoples chain!!!:p

[sschefer]

My guess comes from the use of lightweight flywheels in autos so this might just be completely off track.

A lightened flywheel reduces rotating mass and therefore will spin up faster. It will also spin down quicker due to lower mass inertia.

Under loaded conditions the lighter flywheel will provide less mass inertia to assist in carrying the load.

In theory, if you prop down and use a lightweight flywheel you should get a better hole shot but top end will suffer. It would be a lot like running a vented prop.

If you prop up you're hole shot will go to heck but your mid to top et's should be significantly lower since the engine itself would be loaded lighter at that point. Max RPM should increase some with a lighter flywheel and it might be enough to give you the edge over the competition but I don't think it would be a huge benifit to anyone that is not in running racing environment.

Asthetically, the really look a lot cooler! If someone would just make a production clear cowling I might put one on or at least paint mine a cool color.

[T-REX]

I thanl tha CI's kumz into play when Flywheels are a factor...OB's should be tha same az cars in this aspect ov it...

Back when we run tha Hemi's in SS, we run a 42# flywheel(wit a 5speed doug nash/use'in 4 geers)...We could stab tha throttle, and RPM's would jump quite rapidly(426ci).....Now, we had a fren from around southern mississippi that ran a early model vette, wit a 265 small block, and a 50# flywheel(wit a 5 speed tranny)....He had to start building rpm when he broke the first beem, or he wouldn't ever git it up to it'z launch rpm!!!!...And when He kill'd tha mota, it would take 5 minutes for it to die(seem'd like it anyway).....

In this same senerio, If we both ran 25# flywheels, the 265 wouldn't take off, but tha bigger CI mota would...Now, Tha Vette run MP and we run SS, so tha HP ov tha 2 motas were not far apart, with torque bein tha major factor ov what tha flywheel needs to weigh!!!!.....I no this don't dictate which flywheel to run on a OB, but juss sheds another lite on anuther factor ov which flywheel to use and why......Hemi crankz takes poundings that OB cranks only dreem about(size for size)...and yes, hemi's will sholy see 9K+, wit pissonz dat weigh az much az 2.5 blocks..Lol

[powerabout]

Simple physics says it gunna take more power/time to spin up a heavier flywheel.
Whether you can measue that or not is a different matter.
Less gyroscopic force applied to the crank when it axis is inclined must also be true.

[[email protected]]

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

Is this why some motors have an intermittant rumbling noise or as I have heard described as "harmonics in the engine" when in gear idling? The rumbling disappears once a bit of throttle is applied. But is there again once RPM's returned to normal idling.

[catfish123]

I find the minuscule difference on my 225X/XB2003 to be noticeable beyond a reasonable doubt.................LOL

[T-REX]

Is this why some motors have an intermittant rumbling noise or as I have heard described as "harmonics in the engine" when in gear idling?

Tha idle rumble iz usually a geercase, or crank rattle(if idled low enuff)...I thank tha harmoniks would be differnt on each engine...

I had a stockie 200 XRI mota that ran quite smooth wit tha 40 amp system...I changed it over to 16amp, wit aluminium FW...at 3800-3900rpm, it started a weird rattle'in noise(I hate new noises)...I thunk tha damm mota wuz kumm'in apart or sumpth'in...I wuz tell'in a fren ov mine(ole merc guru) and he told me it wuz tha flywheel doin it!!...Well, bien tha hardhed I am, I put a steel flex wheel on it, and tha noise not only moved from that rpm, but it even had a differnt sound!!!.....Put tha aluminium wheel back on and tha noise reappear'd at thaa same rpm!!!....Yup, Harmoniks iz alive and well, but God only know's wher it will be on a given mota!!!...But datz juss my unprofessional opinion:thumbsup:

[LARRY D]

I thanl tha CI's kumz into play when Flywheels are a factor...OB's should be tha same az cars in this aspect ov it...

Back when we run tha Hemi's in SS, we run a 42# flywheel(wit a 5speed doug nash/use'in 4 geers)...We could stab tha throttle, and RPM's would jump quite rapidly(426ci).....Now, we had a fren from around southern mississippi that ran a early model vette, wit a 265 small block, and a 50# flywheel(wit a 5 speed tranny)....He had to start building rpm when he broke the first beem, or he wouldn't ever git it up to it'z launch rpm!!!!...And when He kill'd tha mota, it would take 5 minutes for it to die(seem'd like it anyway).....

In this same senerio, If we both ran 25# flywheels, the 265 wouldn't take off, but tha bigger CI mota would...Now, Tha Vette run MP and we run SS, so tha HP ov tha 2 motas were not far apart, with torque bein tha major factor ov what tha flywheel needs to weigh!!!!.....I no this don't dictate which flywheel to run on a OB, but juss sheds another lite on anuther factor ov which flywheel to use and why......Hemi crankz takes poundings that OB cranks only dreem about(size for size)...and yes, hemi's will sholy see 9K+, wit pissonz dat weigh az much az 2.5 blocks..LolVery old wise one. that 2 stroke takes a pounding ever stroke. the hemi takes it every other stroke. so it would be hard to say which one takes the most beating. Also your test don't count. you have to make more than 2 passes above 8000 rpms to find out if there better. :Dlater Larry D

[Mark75H]

Simple physics says it gunna take more power/time to spin up a heavier flywheel.
Whether you can measue that or not is a different matter.
Less gyroscopic force applied to the crank when it axis is inclined must also be true.


By itself this is correct ... however we are not "flywheel racing" we are boat racing.

The acceleration load the flywheel presents is not the same in neutral as it is while the motor is moving the boat.

While in neutral 100% of the motor's power is used accelerating itself and the difference in accelerating a heavy flywheel can be easily noticed.

For an example we could say that 2 different flywheels change the acceleration out of gear from 2 seconds to a half second ... a very noticeable difference.

Some motors can run with no flywheel at all (they may not run very slow, but it is possible).

Let us say, also just for example, that the flywheel consumes 5 hp of the 200 when accelerating the motor in neutral for that 1.5 seconds noted above.

Now, lets consider the fastest possible acceleration of the boat with the same power ... for this example use 15 seconds from idle to top speed for a pretty fast boat ... 10 times as long.

Horsepower is a function of time and torque ... so when you increase time, you decrease measured horsepower by the same rate.

The same flywheel change that affected the motor at 5 hp in neutral now takes less than a half hp while moving the boat (and note that this is a VERY fast boat, a slower boat will be even less affected) ... but now you should also see that a boat accelerating from idle to top speed in drag race time still only uses 1 hp of 300+ to accelerate the flywheel while it is also doing the job of moving the boat.

OK, now lets take the flywheels off the race boat and put them on a sporty Screamandfly boat and see what the physics says about power and acceleration from half speed to full ... half the speed increase and half the power used ... one quarter of one horsepower involved.

That is the physics ... anything else is an icon with a yellow flag

[tlwjkw]

Tha idle rumble iz usually a geercase, or crank rattle(if idled low enuff)...I thank tha harmoniks would be differnt on each engine...

I had a stockie 200 XRI mota that ran quite smooth wit tha 40 amp system...I changed it over to 16amp, wit aluminium FW...at 3800-3900rpm, it started a weird rattle'in noise(I hate new noises)...I thunk tha damm mota wuz kumm'in apart or sumpth'in...I wuz tell'in a fren ov mine(ole merc guru) and he told me it wuz tha flywheel doin it!!...Well, bien tha hardhed I am, I put a steel flex wheel on it, and tha noise not only moved from that rpm, but it even had a differnt sound!!!.....Put tha aluminium wheel back on and tha noise reappear'd at thaa same rpm!!!....Yup, Harmoniks iz alive and well, but God only know's wher it will be on a given mota!!!...But datz juss my unprofessional opinion:thumbsup:
:thumbsup:
Done 'bout tha same thing.........
Tha light weight was develoved for tha bearing/crank and WINDING DOWN more so than tha winding up for tha little zig zagin'/round n round hot rods. Windin' up was just a added bonus. Lake motor, hardly noticeable if at all. Stem windin' hot rod just one of many little things that add up. If ya line up next ta someone that has ALL tha little things tickin' and you have a few that arn't ya gonna get ya butt handed to ya...........

[[email protected]]

Quote "Tha idle rumble iz usually a geercase, or crank rattle(if idled low enuff)...I thank tha harmoniks would be differnt on each engine..."
Quote

It did it with a different gearcase as well so it must be the crank? It is more noticeable with a larger diameter prop. I was told that it is harmless and not an indication that there is something wrong with the engine.

[T-REX]

It did it with a different gearcase

I didn't meen tha geercase iz bad, juss that tha backlash ov tha geerz, and tha slack in tha splines ov tha driveshaft will make a chatter'in noise bekause tha mota don't idle SMOOTH(like a car mota)...datz all I meant!!

[[email protected]]

Hey TRex....I didn't take it that way at all. Honestly! LOL Just figured it was process of elimination since the gearcase now has all new internals and it did it with the old gearcase too so logically i figured it had to be the insides ie crank. :thumbsup:

[GTO GEORGE]

On a boat the flywheel weight makes no difference in holeshot: the motor accelerates only as fast as the prop lets it. I have done back to back tests witha heavy wheel and a lite one, using Racepak data, and there was no difference. Two reasons for a lite flywheel in a boat: 1) RPM, do you want a relatively heavy rotating mass designed for 6000 rpm to turn 9500-10,000? Too much stress from centrifugal force. 2) Gyroscopic, the gyro effect wants to stabilize the boat going in one direction, to make a turn or change direction you have to overcome this effect; the heavier the wheel, the harder it is to change direction. This is the best reason for a 15" mid; it moves the gyro effect closer to the water or as they do in motorcycle design, mass centralization. This why a 600cc bike will run circles around a liter bike: the stroke is shorter, the flywheels are less diameter and it's easier for the bike to change direction, ie, leaning right then left.

In a drag car, small motor, heavy car, the heavy wheel stores energy, so that when the clutch is dropped, the big tires and heavy vehicle weight don't bog the motor, the flywheel inertia helps launch the car.

A lite wheel probably helps the upper bearing "live" in a merc, but that bearing support aint to beefy to begin with.

[powerabout]

2) would be true for an inboard but not an outboard
A gyro only resist having its axis inclined not moved.
remember the kids spinning top on the floor, doesn't fall over ( inclining the axis) but is happy to move around

[Chummy]

you'll find all you need to know in this thread:

http://forums.screamandfly.com/forums/showthread.php?t=82654

[powerabout]

Thats a good read
it shows that under a certain weight there is no difference which is what you would expect as the rest of the rotating mass is a bigger issue and the prop load

[lpugh]

Think about this: How much hp would it take to spin a 1000 lb flywheel to 6000 rpm on thirty seconds? Do lighter flywheel help acceleration, Yes, maybe, sometimes, there are many varibles. I can say without a doubt that a 3lb reduction on my 3L 250 improved my hole shot 0 to 40 by 2 seconds, did nothing for the top end. Where the weight is removed is more importent than how much is removed. The further away from center it is the more effect it will have.

[Mark75H]

Think about this: How much hp would it take to spin a 1000 lb flywheel to 6000 rpm on thirty seconds? Do lighter flywheel help acceleration, Yes, maybe, sometimes, there are many varibles. I can say without a doubt that a 3lb reduction on my 3L 250 improved my hole shot 0 to 40 by 2 seconds, did nothing for the top end. Where the weight is removed is more importent than how much is removed. The further away from center it is the more effect it will have.

The HP involved is too low

[Dave S]

I kinda like Tunnas.;) Use the Cheapest option.:cheers: Pay My health care.:p

[tj309]

Thanks Chummy - that post told me exactly what I needed to know (and suspected from the beginning)

[T-REX]

I can say without a doubt that a 3lb reduction on my 3L 250 improved my hole shot 0 to 40 by 2 seconds,

I hope ya don't mind if I call :icon_bs::icon_bs::eek::D

[tlwjkw]

Hell Rex, he may have one of those Yamahaaaaaaaaa's :reddevil: