-
The Z Club relies on the support of it's paid members - join the club or renew your membership here.
Flywheel lightening
- Thread starter jonbills
- Start date
You really need to prioritise your uses however from just my own experience:
In a modified car with a 'cam' and ability to breath through carbs, head, exhaust etc it helps to make the car so much more sporty to drive. It's more responsive and allows you to 'blip' the throttle on down changes which is very rewarding. Of course also it helps the engine to pick up speed during acceleration.
What size clutch are you using 225 or 240mm. I lightened my flywheel by 4lbs which was about the difference in the two clutches so couldn't do a direct comparison of before and after but the engine was very responsive. I think all Z flywheels are the same, about 21lbs.
On a standard car I would expect it to spoil a smooth engine but I've no experience of that.
Last edited by a moderator:
Rob,
Wasn't there a thread recently saying that lightened flywheels are dangerous and you should opt for a "light weight" flywheel instead?
I seem to recall something about risk of failure, the immense energy stored and potentially ripping through the car on failure.
I have no experience of this topic but I do remember a discussion here about it.
Ali K
Wasn't there a thread recently saying that lightened flywheels are dangerous and you should opt for a "light weight" flywheel instead?
I seem to recall something about risk of failure, the immense energy stored and potentially ripping through the car on failure.
I have no experience of this topic but I do remember a discussion here about it.
Ali K
Good point. Yes I'm sure there are dangers and the risk has to be understood. I had mine done by a very respected engineering company and they decided the limit not me. I ran the car for 11 years using 7000rpm every time out and the new owner has done the same for the last 3 years.
Flywheels like the Fidenza are much lighter I think.
I'm inclined to not bother with lighter flywheels or lightened flywheel. To my thinking, it can only make a difference to engine braking or accelerating the engine when in neutral.
I quite like engine braking, and don't have a compelling use case for accelerating the engine faster when the car isn't connected!
I quite like engine braking, and don't have a compelling use case for accelerating the engine faster when the car isn't connected!
Jon, I think you're wrong tbh and a lighter flywheel should give you better engine braking surely i.e. it will slow down quicker. I never had a problem with engine braking and if you have a high C/R that helps.
Last edited by a moderator:
Yes, agree Rob - unloaded engine will slow quicker with lighter flywheel. But I think 'engine braking' describes slowing the car by changing down and letting the engine inertia slow the car. That's how I meant it anyway 
Sent from my iPhone using Tapatalk
Sent from my iPhone using Tapatalk
Yes, agree Rob - unloaded engine will slow quicker with lighter flywheel. But I think 'engine braking' describes slowing the car by changing down and letting the engine inertia slow the car. That's how I meant it anyway
Sent from my iPhone using Tapatalk
A heavier spinning flywheel is going to keep spinning longer whether the engine is 'free' or 'loaded'. Anyway are you suggesting changing down without matching your revs, if so your gearbox won't last long.
What you are effectively trying to do is speed up the engine with the inertia of the car not the engine and your heavy flywheel is resisting it causing the car to slow with the load going through the gearbox. That's what lorries do on downhill gradients.The modern thinking is to do all your slowing using modern effective brakes. RIDDLER will tell you that.
Anyway re your original post - a lightened flywheel will help performance by making the engine more responsive.
The engineer in me has a nagging point that keeps coming to mind - surely by reducing the flywheel mass (think of it as an energy capacitor) then you will be sending all kinds of high frequency transients down the transmission and also into the crank.
Furthermore you are moving the resonant frequency peak and possibility of harmonics into a potentially more frequently reached area that may not be matched to the 'box or diff gearing/number of teeth.
So in essence what I'm getting at is, how do you manage harmful resonance / transients / harmonics (esp at lower revs) when you use less mass on the flywheel?
Do the machine shops do some form of Fourier analysis and decide on the safe limits!?
Ali K
Furthermore you are moving the resonant frequency peak and possibility of harmonics into a potentially more frequently reached area that may not be matched to the 'box or diff gearing/number of teeth.
So in essence what I'm getting at is, how do you manage harmful resonance / transients / harmonics (esp at lower revs) when you use less mass on the flywheel?
Do the machine shops do some form of Fourier analysis and decide on the safe limits!?
Ali K
In theory I'm sure you're right and on a standard car I wouldn't change anything. I like smooth engines running as designed. However if you modify an engine for performance and responsiveness then lots of things are taking you away from the manufacturer's tested and reliable design. It's a compromise.
In practice I had no problem at all.
As an aside I'd like to see 'Freewheels' coming back for smoothness and fuel economy. I know coasting is not considered the thing to do because of control and braking etc but surely that needs reviewing. It seems crazy to me that every time you lift your throttle the car slows down when you don't need it to! Imagine riding a push-bike that did that!
Saab had them on their 2 stroke cars so that when you shut off the engine didn't seize from lack of lube. However they carried it over onto 4 stroke cars too.
I've just been reading this:
http://www.w8ji.com/rotating_mass_acceleration.htm
Seems a very thorough and understandable explanation to me.
I think I'll save my money and stick to a standard flywheel!
http://www.w8ji.com/rotating_mass_acceleration.htm
Seems a very thorough and understandable explanation to me.
I think I'll save my money and stick to a standard flywheel!
Alphabettispaghetti
Club Member
I'd go for it, with a straight 6 you can be quite radical with the engine and it'll still be smooth because of its inherent perfect primary balance.
Brilliant article Jon !! 
One of the most obvious places you feel this is on bicycles. I pay double the price to have 55grammes inner tubes as the additional 100g of the non racing ones is massively noticeable when racing, sprinting or climbing.
I sold my £2k Zipp wheels because all the aero advantage was taken away by the slow acceleration / hill climbing ability caused by all the mass on the outside of the wheels!
http://zipp.com/_media/images/dynamicproducts/WH-808-TU-V2-700-SR-11S-BLK-Hero-A625L.jpg
OK maybe going slightly off topic now into a rant
Ali K
One of the most obvious places you feel this is on bicycles. I pay double the price to have 55grammes inner tubes as the additional 100g of the non racing ones is massively noticeable when racing, sprinting or climbing.
I sold my £2k Zipp wheels because all the aero advantage was taken away by the slow acceleration / hill climbing ability caused by all the mass on the outside of the wheels!
http://zipp.com/_media/images/dynamicproducts/WH-808-TU-V2-700-SR-11S-BLK-Hero-A625L.jpg
OK maybe going slightly off topic now into a rant
Ali K
May be off topic Ali but my eldest lad won a triathlon tonight at Mallory Park so we know about aero and weight on bikes.
Attachments
You must be a very proud father!
Yeh he looks a bit lonely doesn't he, he did win by a good margin. I don't want to take the Thread off topic but I'll post another pic.
Jon so you are going 2.8 with 240mm clutch so if you don't do anything your combined flywheel/clutch weight will be 4lbs heavier than a 225mm. I know it's a longer 'throw' crank but so was the 260Z. Some had 225mm some had 240mm so if you 'lost' 4lbs you would only be back to a combined 225mm weight (which is what I did).
Jon so you are going 2.8 with 240mm clutch so if you don't do anything your combined flywheel/clutch weight will be 4lbs heavier than a 225mm. I know it's a longer 'throw' crank but so was the 260Z. Some had 225mm some had 240mm so if you 'lost' 4lbs you would only be back to a combined 225mm weight (which is what I did).
Attachments
Thanks Rob.
We could definitely run a caption competition with that pic!
Good on your boy. I did a sprint triathlon a few years ago, and wish I could do a lot more, but my knees aren't up to the training now.
My L24 has a 240mm flywheel & clutch already, so it's not new weight. But, there's an engineering shop in the next village over that is said to be good at lightening them, so I might pop in to see how much they want to take a few pounds off.
We could definitely run a caption competition with that pic!
Good on your boy. I did a sprint triathlon a few years ago, and wish I could do a lot more, but my knees aren't up to the training now.
My L24 has a 240mm flywheel & clutch already, so it's not new weight. But, there's an engineering shop in the next village over that is said to be good at lightening them, so I might pop in to see how much they want to take a few pounds off.
So why do you need a new flywheel?