Pros and Cons of a Lightened Flywheel.

[Huw]

Having had to sit through a very intense alcohol fuelled debate in the pub the other evening, on the pros and cons of fitting a lightened flywheel and why I should get one (I’m not convinced in anyway). I would be interested to hear from anyone who has fitted a lightened flywheel and upgraded clutch to their Z (preferably someone who knows what they are talking about and not inebriated) to see what their experiences are.

From what I recall of the debate:

Pros: Better acceleration due to less rotational mass. But only a marginal mod with a large engined car (?)

Cons: Poor drivability for road use especially in standard cars with hunting when pulling away from a standstill with the need for higher revs and having to maintain the revs between gear changes. Plus increased stress on the drive train.

From material available on the net, I can see the benefits for doing this mod in a race or fast road application but I’m not convinced it would benefit a road use car at all. As I see it, the mass of the flywheel produced by the manufacturer of a standard road use car will have been derived as a compromise between drivability and performance.

I would like to know what the real benefits of doing this modification, if any, in isolation to a Z and what the drawbacks would be to the drivability of the car. Bit of an open question, but just interested is all.

Cheers

Huw

 

[SeanDezart]

And also does your car and also your personal driving style warrant an investment over equipment which functions perfectly as the manufacturer intended ?

The proponents of the bogging down and increased stress are as old as the 'don't change to K and N air style filters as they'll weaken the mixture ! Why even change the exhaust, brakes, tyre size and windscreen wipers....?

Remember that a Z/ZX was a mass-produced car made with keeping costs low and to appeal to the mass market with a broad range of owner/drivers, some of whom bought it for looks and not to take corners on two wheels.

I've driven my Zs with lightened flywheels sine 1991, some more prepared than others and we've just finished the grey one with a completely stand engine and a steel-billet lightweight flywheel :

lovely, ticks over beautifully at 800rpm and pulls strong to 6500 : more reactive, arguably what Nissan could have offered to a driver-enviroment euro market as upgrades !

For a standard engine, fit a stage II clutch with it and enjoy - no worries.

BTW, I'm sober.

 

[jonbills]

When i was thinking about it, I read this and decided against bothering.
http://www.w8ji.com/rotating_mass_acceleration.htm

And then I went and got the flywheel lightened anyway ;-)

 

[SeanDezart]

I've had a std one lightened (first green Z) about 22-25% if I remember....but since I'd always go for a billet steel one - kinda safer on your balls AND lighter !

 

[Huw]

Glad to hear you are sober Sean! So a recommended mod after all then?

When i was thinking about it, I read this and decided against bothering.
http://www.w8ji.com/rotating_mass_acceleration.htm

I've read that article and it did put me off fitting one also. But having spent more time reading and mulling and having my arm twisted, I've ordered a billet steel lightened flywheel and a bigger 240mm clutch this evening.

Guess I'll find out if it's worthwhile after all now .

 

[SeanDezart]

So a recommended mod after all then?

But having spent more time reading and mulling and having my arm twisted, I've ordered a billet steel lightened flywheel and a bigger 240mm clutch this evening.

Sureley you already had a 240mm clutch ? Who twisted your arm then ?

And it's only reccomended if you're gonna DRIVE the bitch - poodling around and you won't feel her at her best.

 

[AliK]

Glad to hear you are sober Sean! So a recommended mod after all then?







I've read that article and it did put me off fitting one also. But having spent more time reading and mulling and having my arm twisted, I've ordered a billet steel lightened flywheel and a bigger 240mm clutch this evening.



Guess I'll find out if it's worthwhile after all now .

Would love to hear how you get on / how it changes your car etc!

 

[Rob Gaskin]

............ I've ordered a billet steel lightened flywheel and a bigger 240mm clutch this evening.....

Huw, don't forget to check the height of the clutch from the flywheel - you may need a longer release bearing collar.

 

[Aceman]

This argument raged a lot when I used to strip my old rotary..

Being a rotary (with zero torque below boost kicking in at 3500rpm), a lightened flywheel was deemed more responsive for track use/Sean's (what I would deem, proper) driving style having a quicker pick up.

For the drag strip though, the heavier flywheel worked better as the momentum of that greater mass spinning help when dropping the clutch on launch.

Everyone generally agreed though, if you weren't going to "drive" your car "properly", and just pooled around being quite gentlemanly, it was a waste of money changing what Mazda spent a hell of a lot of money developing.

I guess maybe there's something in that that translates to Zeds?!?

 

[SeanDezart]

Everyone generally agreed though, if you weren't going to "drive" your car "properly", and just pooled around being quite gentlemanly, it was a waste of money changing what Mazda spent a hell of a lot of money developing.

I guess maybe there's something in that that translates to Zeds?!?

We are agreed :

And it's only reccomended if you're gonna DRIVE the bitch - poodling around and you won't feel her at her best.

 

[SKiddell]

I found that the low mass of the aluminium flywheel helps the throttle response in between gear shifts where every tenth counts

 

[SeanDezart]

I found that the low mass of the aluminium flywheel helps the throttle response in between gear shifts where every tenth counts

That's what I believed - the engine remains closer to its optimum rev range and doesn't 'drop-off' cam....maybe not with Mazda very high-revving engines then ?

 

[Huw]

Sureley you already had a 240mm clutch ?

Nope it has a 225mm clutch, 2+2's and Turbo ZX have the bigger 240mm clutch apparently

I will indeed let you know Ali what it drives like.

 

[SeanDezart]

Oh...I thought from the 260Z 2+2 onwards that they were all 240mm - learnt something - thanks.

 

[SKiddell]

I found that the low mass of the aluminium flywheel helps the throttle response in between gear shifts where every tenth counts

It all depends on what you intend to do with the car, potter around, fast road, fast road bit of track etc. If its just potter/road use then you can probably spend the money to greater effect.

Just my 2p's worth

 

[Huw]

Finally drove the car today after taking the plunge and opting for a lightened flywheel. There have definitely been pros and cons in doing this modification, so I thought I would share them.

I opted for an all steel billet flywheel from California Datsuns, not cheap but a nice bit of kit weighing in at just 5.4kg and the shipping was actually reasonable. The flywheel had another benefit that did not become apparent at first, it has optional bolthole patterns and guide-pin holes allowing the use of a wider range of clutch assemblies that standard Nissan.



After much research on which clutch friction plate to use - black organic/Kevlar/ceramic plus all the various stages I/II/II etc. I opted for an uprated clutch kit for a 280ZX turbo with a 240mm friction disk. Which turned out to be a complete mistake.

Come the time for a test drive, the car had chronic clutch judder when trying to reverse out of the garage. First gear was not much better and by the time I went around the block and back to the garage the car had a wonderful aroma of cooked clutch. In short the car was utterly un-drivable.

On dropping the gearbox again to find out what the issues was, I had destroyed the clutch completely and the nice new flywheel was burnt to hell. The clutch was not giving enough clamping force so was bouncing off the flywheel and slipping on pick-up or so I have been told. Luckily the flywheel could be resurfaced so not a total loss.

I ended up going back to California Datsuns for their Stage 1 clutch kit, this has the same black organic friction disk but the smaller diameter plate at 225mm. It only took six weeks to arrive having been lost then found again in customs. The clutch cover however does not have the same bolthole and pin configuration as a standard Nissan clutch cover, thankfully the flywheel has those alternate options allowing it to fit. One thing to note, once you fit the guide pins into the flywheel they are a complete and utter nightmare to remove again.

Despite all the problems, mostly my own fault for ill informed choices, I’m very pleased with the outcome. My 280ZX drives like a different car, its much livelier from a standing start and much better through the gears seemingly having better acceleration. Couple of things to note, got to get used to reduced engine braking and the car will stall if the revs drop too low when pulling away. But these are more to do with me getting used to the set up than any real downside. Not tried it in traffic but I don’t think it should be a problem.

 

[SeanDezart]

Huw.

Sorry to hear of your 'adventures'.

Engine braking should be better not worse.

You're giving lightened flywheels a bad name - surely scared some off whereas I ran one for years and years with no problems....!

Hopefully it'll 'all bed-in' !

 

[Rob Gaskin]

Finally drove the car today after taking the plunge and opting for a lightened flywheel. There have definitely been pros and cons in doing this modification, so I thought I would share them.

I opted for an all steel billet flywheel from California Datsuns, not cheap but a nice bit of kit weighing in at just 5.4kg ................

I opted for an uprated clutch kit for a 280ZX turbo with a 240mm friction disk. Which turned out to be a complete mistake.

Come the time for a test drive, the car had chronic clutch judder when trying to reverse out of the garage. First gear was not much better and by the time I went around the block and back to the garage the car had a wonderful aroma of cooked clutch. In short the car was utterly un-drivable.

On dropping the gearbox again to find out what the issues was, I had destroyed the clutch completely and the nice new flywheel was burnt to hell. The clutch was not giving enough clamping force so was bouncing off the flywheel and slipping on pick-up or so I have been told......

I ended up going back to California Datsuns for their Stage 1 clutch kit, this has the same black organic friction disk but the smaller diameter plate at 225mm...............

My 280ZX drives like a different car, its much livelier from a standing start and much better through the gears seemingly having better acceleration. Couple of things to note, got to get used to reduced engine braking and the car will stall if the revs drop too low when pulling away.....

5.4 Kg is quite light, a standard flywheel is about 9.5. I had mine lightened to about 7.7 so half the reduction. I used a 240mm clutch without a problem (Centreforce 2), however a standard 240mm clutch couldn't cope with my modified engine. Are you sure the reduced clamping was not due to release collar incompatibility (wrong length)? From memory though it's more likely to be the opposite way around.

Engine braking - I got enough engine braking ok, in fact on circuits like Donington a 'blip' and 'down-change' gave me enough retardation for most corners. In theory the engine should slow down quicker as Sean says. Are you noticing a lack of engine braking if you change into a lower gear without matching the revs - if so I can understand?

 

[SeanDezart]

A standard flywheel is 10.45kgs.

Not sure about standard 240mm clutch but my L31 has always and will run a 225mm clutch.

I run a steel billet 4.2kg flywheel.

http://www.ebay.co.uk/itm/LIGHT-WEI...hash=item54059852c2:m:mnaxocHGQjyolDGwvemc21Q

 

[Huw]

Huw.

Sorry to hear of your 'adventures'.

Engine braking should be better not worse.

You're giving lightened flywheels a bad name - surely scared some off whereas I ran one for years and years with no problems....!

Hopefully it'll 'all bed-in' !

Sean

Yes I certainly did have a few 'adventures' as you put it, which were down to poor choices rather than the flywheel its self. Really pleased with the end result as I said. I certainly hope I don't put anyone off if they are considering doing similar, that was not my intention. Just wanted to point out be sure to get the right clutch set up first time around.

The perceived reduction in engine braking and stalling is more than likely down to me and my driving, I only had a short test drive so I need to get used to it. But from the short trip I did have, the positive difference in acceleration from a standing start was great.

As to the release collar Rob, I did check that and it was fine. The guy at the gearbox place I had the flywheel resurfaced at, suggested that the clutch was not engaging properly most probably because the spring rating was not high enough causing it to judder and slip. He also did express his technical opinion on the clutch kit I had bought, but that would get censored if I repeat it here.

Now on to the continuing gearbox 'adventures' which I thought I had fixed. Picking up an S14a gearbox tomorrow so will see how that goes. Something to do over winter.......

Huw