Lightened Flywheels

[Checkbuzz]

Hi guys & Gals

The general consensus appears to be that lightened flywheels are a good thing for turbo cars and (grip) track work but that going too light can be a problem (loss of torque).

I had a reliable source (Jim Berry the clutch man) tell me that the stock flywheel (i.e. not lightened) is the way to go (for turbo Nissans) and not to bother with the lightened items especially the alloy and cro-molly flywheels (due to friction and heat sinking capabilities).

Stock flywheels are 9.6-10kgs and I have been looking at a steel billet NPC flywheel that is 6.8kgs which seems like a good compromise.

I would like to know what peoples thoughts and experiences are with lightened flywheels vs stock and ideal weights for different racing e.g. grip, drift or drags.

Cheers

[djr81]

People who say that a lightened flywheel reduces the amount of torque the car produces are speaking through their collective arses and should be ignored.

For track work run the lightest flywheel you can find. If you can save 3kg on rotating mass then do it.

For drag work run a light flywheel but you have to be able to launch the car & the lighter the flywheel the more sensitive it is to getting the launch rpms spot on. Also you are more likely to have clutch issues so what you have been told makes good sense.

For drifting just cable tie the old busted one together like all the other drift crap. Then talk it up with the aid of incomprehensible hand gestures & a stupid fitted cap worn at an angle.

Edited February 16, 2011 by djr81

[joeyjoejoejuniorshabadoo]

it does have a downside, and that is that what you pick up down low, you lose a lil up top.

it will rev up quicker, but it will drop faster between gears, which is why it's not such a great thing for drift.

it's all about enertia, once something is moving, it takes a certain amount of time to stop, when it's heavier it takes longer to get up to speed, but takes longer to stop. when it's lighter it gets up to sped quickly, but also slows down faster

my best mate and I have near identical cars (same mods/power, and his has a lightweight flywheel, and although the difference is almost not noticeable, i do prefer mine)

[R31Nismoid]

For drifting just cable tie the old busted one together like all the other drift crap. Then talk it up with the aid of incomprehensible hand gestures & a stupid fitted cap worn at an angle.

lol WIN!

[The Dan]

People who say that a lightened flywheel reduces the amount of torque the car produces are speaking through their collective arses and should be ignored.

For track work run the lightest flywheel you can find. If you can save 3kg on rotating mass then do it.

For drag work run a light flywheel but you have to be able to launch the car & the lighter the flywheel the more sensitive it is to getting the launch rpms spot on. Also you are more likely to have clutch issues so what you have been told makes good sense.

For drifting just cable tie the old busted one together like all the other drift crap. Then talk it up with the aid of incomprehensible hand gestures & a stupid fitted cap worn at an angle.

No, I think you might be only considering one aspect of the equation here.

It does reduce stored energy. That is a law of physics.

On the other hand, lighter is always better....ALWAYS......for a track car

If you value the way it drives and feels on the street, then don't go too light. Lighter is not bad, just too light can make it feel shit to drive, especially in traffic.

I can tell you now, having a 3kg flywheel on a street car sucks arse to drive around town.

Having it on a car that sees constant revs above 4k is nothing short of awesome

[djr81]

No, I think you might be only considering one aspect of the equation here.

It does reduce stored energy. That is a law of physics.

On the other hand, lighter is always better....ALWAYS......for a track car

If you value the way it drives and feels on the street, then don't go too light. Lighter is not bad, just too light can make it feel shit to drive, especially in traffic.

I can tell you now, having a 3kg flywheel on a street car sucks arse to drive around town.

Having it on a car that sees constant revs above 4k is nothing short of awesome

Well to be fair that was all he asked about.

I chucked a lightened flywheel in my car & it is still driveable on the street. To put it in perspective a cam change had more of an influence on how it responded off idle than the flywheel weight change.

[PaulosECR33]

do you want to change it cos your standard one is stuffed or cos you want to... i have a billet one in my ute cos i hate dual mass flywheels, revs quicker and dies quicker but i honestly cant say there is any gain in anything, dual mass is like over 15kg and my billet one is 9. there are plenty better things to get other than a lightened flywheel unless you have done everything else and are shaving seconds off time...thats my opinion

[Checkbuzz]

Thanks for the feedback guys!

@djr81 - ROFL! It isn't for drifting mate but thanks I love the comments

I do realise that flywheels don't affect the actual torque produced by the engine but they do affect how that torque is applied to the wheels, which for all practical reasons is what really matters.

@PaulosECR33 -I am upgrading the flywheel because I am upgrading the clutch, and replacing the rear main seal etc.

This car is no longer my primary drive so will be more track focussed from now on. I believe in doing a job once, doing it properly and getting the car fit for purpose. The original flywheel would have to be removed and machined anyway so the cost of a new flywheel is really peanuts in the scheme of things... I just want to make sure I get the right one.

So it looks like the steel billet 6.8kg flywheel will be a good compromise between street and track as well as ticking all the boxes for friction and heat-sinking capabilities.

Edited February 16, 2011 by Checkbuzz

[Birds]

$40 to machine a flywheel and any decent mechanic would do the removal/re-install of it as part of the clutch change labour. Stick with the standard one IMO. Unless you're changing gears too fast for the revs to drop, there's no need lighten her up. Naturally aspirated vehicles respond better to lightened flywheels due to less variables impacting engine response; the power band is also much more linear. Turbocharged vehicles need more revs to get off the line as it is, you need all the kinetic energy transfer you can get. Lightened flywheel = slip the clutch more or give it higher rpm on take off, therefore wearing the clutch faster. All relative to how much lighter the flyheel is, of course. But it's a much more pleasant drive to have some kinetic energy stored up in the driveline and retain a better balanced engine. Heavier flywheels are also better at silencing engine and clutch "noise" (vibratons).

Best way to think of a flywheel is those toy cars you push and they don't slow down for a while...they have a small flywheel in them...without it, or with a lighter one, they lose momentum much faster and the motion of the toy car is not as smooth/consistent. Not something you want in a street car - you don't always change gears fast and the rev matching can drive you nuts around town if it's too light!

In a dedicated track car though...go nuts...you spend 99% of the time above 5000rpm and you only have to launch it once (hopefully!). Just make sure it's a good quality flywheel cause I've seen plenty of steel billet / chrome moly "flyIng" wheels

[bigmikespec]

^^^ so why dont we have massive heavy flywheels if we "need all the kinetic energy transfer you can get".

If you are changing a clutch put a lighter one in, if you are not doing the clutch then leave it. Ligher flywheel will always be faster through the revs, I do not believe for a second that the revs drop so fast through the gears that it is an issue... besides, you have a ligher flywheel and the engine can overcome the interia to speed it back up again!

[Messiah]

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.

[Birds]

^Yes, remember the golden rule when it comes to modifications: for every upside, there is a downside. Faster through the revs sounds like a good thing, in many situations it's not. A heavy flywheel keeps things running smooth, like a low idle for instance. Diesels in general have heavy flywheels because they need more stored up energy to balance the movement of the engine and allow them to idle at very low RPM. Engine has enough torque to do it, but not smoothly without a heavy flywheel. In a track car these things don't really matter.

[djr81]

^Yes, remember the golden rule when it comes to modifications: for every upside, there is a downside. Faster through the revs sounds like a good thing, in many situations it's not. A heavy flywheel keeps things running smooth, like a low idle for instance. Diesels in general have heavy flywheels because they need more stored up energy to balance the movement of the engine and allow them to idle at very low RPM. Engine has enough torque to do it, but not smoothly without a heavy flywheel. In a track car these things don't really matter.

All a flywheel does is store energy. So yes a heavy flywheel stores more energy as the motor moves up through its rev range than a light one. But when you put your foot on the brake that energy is converted to heat. So clearly in a track car (part one of the original question) there is really no downside of having a lightened flywheel.

A flywheel doesn't balance movements. It dampens them. A straight six (like in oh, say a skyline) has a balanced motor whereas a POS Emo has a four which has a second order harmonic that only a pair of Lanchester balancers can ever remove.

So yes your bucket of bolts four cylinder diesel may well benefit from a heavy flywheel. But really, so what?

[Nanogrip]

You would also need to have the harmonic balancer/crank pulley checked if you choose to use a lightened flywheel from what I understand. Otherwise the engine could damage itself in time by the unbalanced rotational forces acted on it. Dunno, read it somewhere a long while ago.

[Birds]

^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.

All a flywheel does is store energy. So yes a heavy flywheel stores more energy as the motor moves up through its rev range than a light one. But when you put your foot on the brake that energy is converted to heat. So clearly in a track car (part one of the original question) there is really no downside of having a lightened flywheel.

A flywheel doesn't balance movements. It dampens them. A straight six (like in oh, say a skyline) has a balanced motor whereas a POS Emo has a four which has a second order harmonic that only a pair of Lanchester balancers can ever remove.

So yes your bucket of bolts four cylinder diesel may well benefit from a heavy flywheel. But really, so what?

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.

In a track car these things don't really matter.

In a track car these things don't really matter.

In a track car these things don't really matter.

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.

[djr81]

Calm down dude. You will burst a blood vessel or something. Hug?

Actually I wondered wtf Nissan are thinking when I was looking at a busted Lanchester balancer in the sump of a 4 cylinder diesel in a Navara.

[bigmikespec]

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.

That is a stupid analogy.

The way you go on about it Birds you make it sound like it is the most critical part of an engine... it is simple. You need one for the clutch pressure plate and starter motor and not excessively light that it will cause throttle control issues (of which I have not heard a lot of/if any in modified GTR's with light flywheels). Not sure about balance and dampening though?

[MBS206]

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...

[Birds]

That is a stupid analogy.

The way you go on about it Birds you make it sound like it is the most critical part of an engine... it is simple. You need one for the clutch pressure plate and starter motor and not excessively light that it will cause throttle control issues (of which I have not heard a lot of/if any in modified GTR's with light flywheels). Not sure about balance and dampening though?

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.

[waxracing]

Seriously guys you are over complicating things.

The stock flywheel is heavy enough to allow grandma to go the hairdresser and get her purple hair die put in with out pig rooting off the line.

If thats you then cool go for it.

A lighter one will be more sensitive coming off the line but its not like you are making a flex plate out of it so dont worry.

I laughed when i read the one about a heavy flywheel helping you go up hill. yeah maybe if you are in a diesel but as long as the hill is not so steep you cant accelerate up there then its not an issue. Im sure thats close to about 80 degree hills. I havent seen many of those but sure would like to. I wonder if they run massive flywheels on hill climb cars