Lightened Flywheels

[joeyjoejoejuniorshabadoo]

i actually change flywheels when i drive up hills.... i have a special lead one that i keep in the boot

[Messiah]

never said it helped you drive up a hill, i used it as an example if a time when using a heavy rotating mass to maintain revs is beneficial.

I also balanced it out with the counter point of taking more effort to spin up.

My main aim was to counter some of these knobs who keep claiming that there is no point to a standard weight flywheel.

some of you keyboard warriors just hate people dissagreeing with you dont you.

[waxracing]

actually a lighter flywheel will rob you when in high load situations such as climbing steep hills.

never said it helped you drive up a hill,

some of you keyboard warriors just hate people dissagreeing with you dont you.

You can understand our confusion

[Messiah]

yeah i can see where that could baffle you, but i can also see that its not wrong.

it was given as an example of a situation where energy stored in a heavy rotating mass is of benefit. and as i also mentioned in that same post that it has its draw backs.

if i'm wrong, and the effect mentioned does not occure in reality then i thank you for correcting me, if not....

The main point of my post was to counter big mikes sarcastic statement of "well why doesnt everyone just put the heafiest on they can in?" as though there was no point to the factory wheel.

Myabe i should have just said the opposite in equally sarcastic tone.

but in the end its all the same... yes lighter has advantages, as mentioned, it also has its drawbacks... as mentioned. they both do.

let the OP underastand the physics and make up his own mind based on what he thinks is best is my approach

[waxracing]

Its all good I know what you meant.

Im just being a stiring prick

[The Dan]

actually a lighter flywheel will rob you when in high load situations such as climbing steep hills. Whilst your revs will fall no matter what with enough load placed on the engine, a heavier fw will slow this drop in rpm sometimes avoid the need to drop a gear.

so to correct bigmike here... you engine will over come the inertia and speed it back up again except in cases where it doesnt have the grunt to, you know those situations flywheels are designed for.

so normal fly wheel means slow dropping on revs while remaining in gear... lightened means having to drop a gear.

Flip side is normal means greater rotating mass to spin when accellerating, lightened means lower mass so quicker on the flat or in low gears.

^Yes it certainly can upset the balance of an engine. Flywheel works with the harmonic balancer to counter the effects of the drive pulleys and vibrations / forces acting on the crank in general. Gearbox too.

1. Flywheel doesn't just store energy, it releases energy too, along with a whole line of other important jobs e.g. start the friggen car. Very important not to forget its role in the drivability of a car.

2.

3. It balances and dampens, pick a word to describe the role/s, whatever, try running an engine without a flywheel and see how balanced/stable that sucker feels. Better have some good throttle control!

4. So what? Why even have a flywheel at all? What were Nissan thinking? Why do they bother with dual mass flywheels when a lighter single mass will suffice?

L/2 flywheel.

These guys get it. 100% correct

To all you girls out there, I ran a 4.5KG moly flywheel behind my 25 for over 12 months without an issue, driven daily, on the streets. Never a single little problem up and down hills, was quick to rev out, not an issue.

I have no idea about you guys, but I never get to a hill where I'm flat to the floor going "f**k! I WISH I HAD A HEAVIER FLYWHEEL!", actually, to be honest, I barely ever changed throttle position to climb hills and never lost speed... It drove basically the same as my mates stock R33 when going up and down hills.

I'm sorry, but give me a lightened fly wheel any day... Remember, for every KG of rotating mass, you're removing around 10KG of static mass in comparison...

IE, remove 8KG from the rotating setup, and you've dropped the vehicle weight affectively by 80KG... I'll take that on the street and track any day of the week...

You're only looking at one aspect of the equation

Most critical? No. Critical? Yes. Your car won't go far without one. That sounds critical to me. As for balancing and dampening, perhaps you would like to explain the existence of harmonic resonance that often develops when you replace dual mass flywheels for single mass? I'd be happy to upload a sheet from my clutch supplier stating so. Believe it or not, they are an engineered part of the engine...both shape and weight are chosen variables, it is no accident.

Yes, the dual mass flywheel is designed to remove resonance but it is also tuned to the car. The manufacturer engineers spring strength and cushioning into the DMF according to engine harmonic at various torque areas, drivetrain resonance and even things like tyre size and diff ratios etc.

Flywheels do more than attach your clutch to the back of your engine so the guy who suggested that, stick to your day job as you clearly missed the point

[NYTSKY]

We have just put a 6.8kg 4140 one-piece billet chromoly steel flywheel on the back of my motor.

I hope i dont encounter too many hills

[ssxRicho]

The current skyline has a machined stockie, compared to the exedy light unit this feels like I'm carrying a fat chick around on my right foot.

[bigmikespec]

Most critical? No. Critical? Yes. Your car won't go far without one. That sounds critical to me. As for balancing and dampening, perhaps you would like to explain the existence of harmonic resonance that often develops when you replace dual mass flywheels for single mass? I'd be happy to upload a sheet from my clutch supplier stating so. Believe it or not, they are an engineered part of the engine...both shape and weight are chosen variables, it is no accident.

I call that bluff... upload the sheet, lets keep this thread interesting

I do not believe it is that critical in a I6.

[NYTSKY]

[Messiah]

yes you've just proven what everyone here already knows, that a ligthened wheel spins up and down faster.

but you seem to be working hard to avoid the facts, or tell me i'm wrong outright.

so to call my bluff, care to put it on the record that you completeley disagree and that changing the weight of a fly wheel has abosolutely no effect on the conservation of engine momentum (which to drive the point home, will require a change of gear to rectify if severe enough) and as such does nothing to assist a motor in high gear situtions when the gearing is not ideal for the situation... for example only.. cruising along in 4th/5th and encountering a moderatly steep incline.

my experience is that your revs will die off in any case, but slower in the car with a heavier flywheel, possibly negating the need to shift down.

I'm not contesting the benefits of a ligthened wheel, i know them just fine, only pointing out the downsides that can and do occur.

[waxracing]

If your just cruising then they will drop off quicker. If you put your foot down they will build quicker.

if you want to go slowly up a hill seeing if you can get your rpm low enough that your oil light flashes then yes a heavier flywheel is a better thing, But then so is a bull dozer

[bigmikespec]

yes you've just proven what everyone here already knows, that a ligthened wheel spins up and down faster.

but you seem to be working hard to avoid the facts, or tell me i'm wrong outright.

so to call my bluff, care to put it on the record that you completeley disagree and that changing the weight of a fly wheel has abosolutely no effect on the conservation of engine momentum (which to drive the point home, will require a change of gear to rectify if severe enough) and as such does nothing to assist a motor in high gear situtions when the gearing is not ideal for the situation... for example only.. cruising along in 4th/5th and encountering a moderatly steep incline.

my experience is that your revs will die off in any case, but slower in the car with a heavier flywheel, possibly negating the need to shift down.

I'm not contesting the benefits of a ligthened wheel, i know them just fine, only pointing out the downsides that can and do occur.

Not disagreeing because that is basic engineering principal... as far as dampening and balancing I do not believe it has a significant effect considering the I6 configuration (negating the R34 dual mass BS).

The argument is downsides are insigificant to warrant keeping a heavier flywheel; why would you want one in a performance car? Is anyone really concerned with changing gear driving up a hill? I do not think so!

[MBS206]

yes you've just proven what everyone here already knows, that a ligthened wheel spins up and down faster.

but you seem to be working hard to avoid the facts, or tell me i'm wrong outright.

so to call my bluff, care to put it on the record that you completeley disagree and that changing the weight of a fly wheel has abosolutely no effect on the conservation of engine momentum (which to drive the point home, will require a change of gear to rectify if severe enough) and as such does nothing to assist a motor in high gear situtions when the gearing is not ideal for the situation... for example only.. cruising along in 4th/5th and encountering a moderatly steep incline.

my experience is that your revs will die off in any case, but slower in the car with a heavier flywheel, possibly negating the need to shift down.

I'm not contesting the benefits of a ligthened wheel, i know them just fine, only pointing out the downsides that can and do occur.

In any car I'm driving, I'll drop a gear BEFORE the hill to put the revs in a nice meaty part of the torque. I don't let my engines sit and labour, that's not good for other things... High load, low RPM is a detonation prone point, as well as a fuel thirsty if you're climbing hills...

But to be honest, a stock R33 has 150 odd RWKW on tap... It doesn't take that much power to climb a steep hill that is on the freeway.

4.5KG flywheel and I still managed to head up and down the Hume highway Wollongong - Goulburn without needing to drop gears... And they've got some decently steep hills...

Maybe if you're driving your mums 1980 model civic and encounter a hill, you'll want the heavier flywheel... In something that can punch enough torque... Well you're kidding yourself really that the light weight flywheel f**ked your ability to go up hills easily.

On the topic of harmonics... HOW can it dampen harmonics? It's a solid plate of steel... Notice how anything that is a DAMPENER has a way to sustain and miniise shock waves? IE, rubber, or a fluid... Say like, in a harmonic balancer?

[The Dan]

In any car I'm driving, I'll drop a gear BEFORE the hill to put the revs in a nice meaty part of the torque. I don't let my engines sit and labour, that's not good for other things... High load, low RPM is a detonation prone point, as well as a fuel thirsty if you're climbing hills...

But to be honest, a stock R33 has 150 odd RWKW on tap... It doesn't take that much power to climb a steep hill that is on the freeway.

4.5KG flywheel and I still managed to head up and down the Hume highway Wollongong - Goulburn without needing to drop gears... And they've got some decently steep hills...

Maybe if you're driving your mums 1980 model civic and encounter a hill, you'll want the heavier flywheel... In something that can punch enough torque... Well you're kidding yourself really that the light weight flywheel f**ked your ability to go up hills easily.

On the topic of harmonics... HOW can it dampen harmonics? It's a solid plate of steel... Notice how anything that is a DAMPENER has a way to sustain and miniise shock waves? IE, rubber, or a fluid... Say like, in a harmonic balancer?

You seriously need to do more reading

And to the others, he's not talking about making the skyline flywheel heavier to go up hills. The flywheel it has is perfectly matched to the size and power of the engine in standard form. It's an engineered part of the car as he said. Everyone focusing on the 'I can't feel it so it mustn't be there' idea, really shouldn't be commenting because they have no idea what they are talking about

[karma_syke]

i've enjoyed reading this thread, i'd like to see a point someone raised earlier explained more throughly, they claimed that taking ~4.5 kg out of the rotating mass is like taking 80kg off the stationary mass,

a) is this principle true, (point to supporting evidence plz)

b) if it is true, why is this getting overlooked, 80kg is very significant. thats like lightening the car 5-6%

[Shazza24]

In truth you would be better off having a car that has golf ball like dimples all over it because after 60km/h wind resistance is quite a factor (ever wondered why the don't use perfectly round golf balls) but even this is still only one part and off topic.

The below is taken from: http://hpwizard.com/...al-inertia.html

Flywheels

This section is the most complicated and hence the most long winded. My apologies in advance. First off, a change in flywheel may effect revability, ease of speed matching shifts, ease of pulling away from a stop, NVH, etc...none of which will be discussed here. So, that having been said, how does a lightweight flywheel help in terms of acceleration? In short, a lot...or not at all. Bear with me for a second.

We're staged at the tree, in first gear, engine near redline, clutch pedal on the floor ready to be side-stepped, warranty ready to be voided. Light goes green, we side step, RPM drops, car surges forward, RPMs climb again, clutch starts smelling expensive. What has happened in that short time is that we've converted the rotational energy stored in the flywheel to forward motion. Now we're trying to spin it up again. To a lesser extent, this happens at EVERY gear change. The energy stored in the flywheel goes towards spinning up the rest of the drive train and moving the car forward, and then the engine works to spin the flywheel back up to near red-line speeds. So is it better to reduce or increase the inertia of the flywheel? Before we answer that, a few points:

• Not all flywheel energy is converted to forward motion. Some is lost to clutch slip, in the form of heating and ablation of the clutch disk. How much is lost? Depends on the speed difference of the clutch face and flywheel, the condition of the flywheel surface, the grippiness of the clutch, the speed of the shift, and some other factors I'm probably forgetting. Some of the energy is also lost to engine friction, in the form of RPM drop between shifts. So there's no definite answer to this question. As such, I've left it open in the calculator below. "Recovery Percentage" is the percent of flywheel rotational energy that gets converted to forward motion after each shift. Take your best guess. Also note that even if 100% of the flywheel energy is transferred to the drive train when you shift up, you're still likely to lose some of that energy to instantaneous wheel spin (aka "chirp").
• A heavy flywheel can load the engine. This is not necessarily a bad thing. If your car is turbocharged, you can load it against the flywheel to help spool the turbos before launching...assuming your timing is good enough. And for a car with a narrow power band, the flywheel can help keep the engine in the sweet spot between shifts.
• The flywheel energy stored in first gear is "free". "Free" at the drag strip, anyway. Meaning time and energy spent spinning up the flywheel when staging doesn't count against your E.T. In fact, in the extreme case, a huge flywheel could actually make your car quite a bit faster. For instance, take a 3000lb car with a 100hp engine and an enormous flywheel. You could theoretically run a 10 second quarter mile...if you were allowed a few minutes to spin up the flywheel in the staging lane, and could find a way to dump the stored power without breaking anything. Like I said, this is an extreme example just to make a point. Flywheel energy storage systems can have tremendous power to weight ratios, but are a challenge for mobile applications due to gyroscopic forces and safety concerns.

All that having been said, the calculator below will show you that the equivalent mass of the flywheel is HUGE, especially in lower gears. It's not uncommon for the equivalent mass of a flywheel to be 10x its static mass. Mitigating this somewhat is the fact that the equivalent mass is most significant in 1st and 2nd gears, and you may be traction limited there anyway.

This calculator will display the results in two forms. The first is a raw equivalent mass calculation for each gear. This gives the equivalent mass assuming you accelerate from 0 RPM to redline in only one gear. Not terribly realistic, but it shows the diminishing effects of flywheel rotational inertia in higher gears.

The second presentation is "constant equivalent mass", for lack of a better phrase, and is a bit more meaningful. This accounts for launch RPM (free flywheel energy) and the recovery of energy between shifts, at whatever percentage you specify. The equations are a bit involved, so I'll explain by example instead. Bear with me on this one...

Let's say you have a 20 gallon water tank in your car. Accelerating it from idle to redline in first gear (say 30 mph) takes a certain amount of work. As you shift in to second you trigger a quick dump valve, leaving you with 12 gallons of water in the tank. In second gear you accelerate this mass of water from 30 to 60 mph. Now you shift into third, and dump 7 more gallons. You accelerate the remaining 5 gallons of water from 60 to 90 mph, and we'll stop there for now. Accelerating this variable mass of water from 0-90 mph took a certain amount of energy. The constant equivalent mass is the CONSTANT amount of mass that takes the same amount of energy to accelerate from 0-90 mph. Note that it's more than a simple average, since it takes into account the relative gear ratios, the energy recovery, and launch RPM.

Hope this helps!

Edited February 20, 2011 by Shazza24

[Birds]

^^^Very good article explaining it much better than I could. I love the analogy about the 100hp engine on a drag strip. And I agree with Dan...more reading on flywheels needs to be done by a few people. It's not good enough that you'e driven your cousins Skyline with a lightened flywheel...I don't care...I've seen this stuff on a weekly basis. As car enthusiasts we often make exceptions for the modifications we do...but it's all very subjective. Some enthusiasts dig a locked diff and a 5 puk button clutch...and call others pussy for not liking it. Others prefer the standard feel - same goes for flywheels. I used to have customers return because they didn't like the feel of their lightened flywheel or the resonance it left behind. So I would never recommend a lightened flywheel to everyone because it isn't for everyone, and there is a downside to it.

I call that bluff... upload the sheet, lets keep this thread interesting

I do not believe it is that critical in a I6.

I6 may be a well balanced configuration compared to others, but it is not void of inertia, particularly in a 10-20 year old car with worn tolerances. The harmonics themselves are brought about by rotational forces...it's only natural that the forces of a rotating object heavy enough, and attached to the same rotating part/s causing the harmonic, can affect said harmonics. When you take some weight out of the object, you're changing the whole equation - sometimes this can leave you with a resonance.

[djr81]

Seeing as some of you want numbers, here are numbers:

Take the case of (for example) an R32 GTR. Weighs 1600kg with drivers & fuel.

It travels at 72km/h. Why 72km/h? Because it gives you nice simple numbers to work with when converted into other units.

Things to know:

Kinetic Energy (Linear) = ½ * mass * velocity squared.

This is how we represent the energy of the car travelling in a straight line. Like all energy it is measured in Joules.

Rotational kinetic energy (ie flywheel) = ½ * rotational inertia * angular velocity

Rotational inertia is for the flywheel, obviously.

For a cylinder (which is what the flywheel can be represented as, albeit a very short one)

I = ½ * mass * radius squared.

Angular velocity is engine speed, measured in radians per second (Not rpm)

SO:

Kinetic energy = ½ * mass * velocity squared

=1/2 * 1600 8 20^2

=320,000 Joules.

Rotational inertia of the flywheel calculation.

Mass = 10kg.

Radius = 0.2metres (Approx)

I = ½ * 10 * 0.2^2

= 0.2kgm^2

Rotational velocity of flywheel.

GTR does 28.5 km/h per 1000rpm in fourth.

ie 72 km/h = 2500rpm.

2500rpm = 265 radians per second.

Rotational kinetic energy calculation

E ® = ½ * rotational inertia * angular velocity

=1/2 * 0.2 * 265^2

=7000 Joules.

So the amount of kinetic energy in the rotating flywheel = 7000 Joules

The amount of kinetic energy in the car = 320,000 Joules.

Or to put it another way 2%.

So a 3kg lighter flywheel will be less again, about 1.4%.

If you think you can feel or even measure a 0.6% difference you are dreaming. It is the equivalent of 10kg of dead weight.

So what does this all mean?

The major difference in the flywheel masses are the following:

1. With a heavier flywheel there is more rotational inertia in the engine which is felt when the clutch is in. This extra inertia feels better when you pull away (slowly) from the lights. It also acts as a mass damper to make the engine idle smoother. In other words it makes Nanna happy.

2. A lighter flywheel stores less energy than a heavier one. If you have a track car energy stored in the flywheel is energy not used to make the car go quicker. So you run the lightest flywheel you can.

3. The importance (or otherwise) of flywheel mass is larger in lower gears as the engine is rotating faster relative to the cars speed. When the car is in gear you cannot tell how heavy the flywheel is.

[The Dan]

Seeing as some of you want numbers, here are numbers:

Take the case of (for example) an R32 GTR. Weighs 1600kg with drivers & fuel.

It travels at 72km/h. Why 72km/h? Because it gives you nice simple numbers to work with when converted into other units.

Things to know:

Kinetic Energy (Linear) = ½ * mass * velocity squared.

This is how we represent the energy of the car travelling in a straight line. Like all energy it is measured in Joules.

Rotational kinetic energy (ie flywheel) = ½ * rotational inertia * angular velocity

Rotational inertia is for the flywheel, obviously.

For a cylinder (which is what the flywheel can be represented as, albeit a very short one)

I = ½ * mass * radius squared.

Angular velocity is engine speed, measured in radians per second (Not rpm)

SO:

Kinetic energy = ½ * mass * velocity squared

=1/2 * 1600 8 20^2

=320,000 Joules.

Rotational inertia of the flywheel calculation.

Mass = 10kg.

Radius = 0.2metres (Approx)

I = ½ * 10 * 0.2^2

= 0.2kgm^2

Rotational velocity of flywheel.

GTR does 28.5 km/h per 1000rpm in fourth.

ie 72 km/h = 2500rpm.

2500rpm = 265 radians per second.

Rotational kinetic energy calculation

E ® = ½ * rotational inertia * angular velocity

=1/2 * 0.2 * 265^2

=7000 Joules.

So the amount of kinetic energy in the rotating flywheel = 7000 Joules

The amount of kinetic energy in the car = 320,000 Joules.

Or to put it another way 2%.

So a 3kg lighter flywheel will be less again, about 1.4%.

If you think you can feel or even measure a 0.6% difference you are dreaming. It is the equivalent of 10kg of dead weight.

So what does this all mean?

The major difference in the flywheel masses are the following:

1. With a heavier flywheel there is more rotational inertia in the engine which is felt when the clutch is in. This extra inertia feels better when you pull away (slowly) from the lights. It also acts as a mass damper to make the engine idle smoother. In other words it makes Nanna happy.

2. A lighter flywheel stores less energy than a heavier one. If you have a track car energy stored in the flywheel is energy not used to make the car go quicker. So you run the lightest flywheel you can.

3. The importance (or otherwise) of flywheel mass is larger in lower gears as the engine is rotating faster relative to the cars speed. When the car is in gear you cannot tell how heavy the flywheel is.

Radius should be 0.25-0.26m roughly as the clutch plate itself is 240mm in a standard skyline. I'm surprised you overlooked this as you clearly went to a lot of trouble with your cut and paste