Lets Talk Flywheels
Discussion
My personal choice would be to go with the lightest flywheel you can. As mentioned above, the other rotating components all have significant mass, and don't forget you have 4 firing events per revolution smoothing things out, it's hardly an ATCO mower or Fiat 126.
You can also ramp up the ignition map below idle on closed/light throttle to increase the power below idle and prevent stalling too.
The energy stored in the flywheel may help you when pulling away, but a heavier flywheel will only inhibit the acceleration rate thereafter, meaning more energy used to accelerate the car and more fuel required than with a lighter unit, though I accept that this is a law of rapidly diminishing returns.
You can also ramp up the ignition map below idle on closed/light throttle to increase the power below idle and prevent stalling too.
The energy stored in the flywheel may help you when pulling away, but a heavier flywheel will only inhibit the acceleration rate thereafter, meaning more energy used to accelerate the car and more fuel required than with a lighter unit, though I accept that this is a law of rapidly diminishing returns.
spitfire4v8 said:
My personal choice would be to go with the lightest flywheel you can. As mentioned above, the other rotating components all have significant mass, and don't forget you have 4 firing events per revolution smoothing things out, it's hardly an ATCO mower or Fiat 126.
You can also ramp up the ignition map below idle on closed/light throttle to increase the power below idle and prevent stalling too.
The energy stored in the flywheel may help you when pulling away, but a heavier flywheel will only inhibit the acceleration rate thereafter, meaning more energy used to accelerate the car and more fuel required than with a lighter unit, though I accept that this is a law of rapidly diminishing returns.
Point taken, I respect your opinion and experience in these matters.You can also ramp up the ignition map below idle on closed/light throttle to increase the power below idle and prevent stalling too.
The energy stored in the flywheel may help you when pulling away, but a heavier flywheel will only inhibit the acceleration rate thereafter, meaning more energy used to accelerate the car and more fuel required than with a lighter unit, though I accept that this is a law of rapidly diminishing returns.
For now I'm very comfortable with my 19lbs choice, and I'm confident it's right for my needs.
But as the engineer who's making my flywheel said...
"I can always easily spin your 19lb flywheel down to 15lbs at a later date, but if you take the 15lbs one off the shelf and you don't like it there's no option to add material back on"
He also suggested letting me try the 15lb one in the future and taking my 19lb one in exchange if I liked it better, or taking the 15lb one back at no charge if I didn't.
The real way to find the best weight for an individual's tastes and driving style would be to take sacrificial flywheel and keep shaving half a pound off it at a time, until you found the point at which you went half a pound too light.
You could then have a new flywheel made to the exact weight that sits just the right side of the lightest point where sufficient drivbility is retained.
Of course flywheel weight is all subjective, what's considered the perfect weight will vary greatly from driver to driver and from car to car, one man's too light is another's way too heavy.... and vice versa.
Lets see how I get on with my bespoke 19lb cut, one thing is for sure it'll definitely be a good 6lbs better than what I have now, and what I have now was already a massive improvement over the original and comically heavy millstone.
And best of all..... I still have option to go lighter from there if I ever feel the need to do so
UPDATE
This morning I popped out to the garage and weighed my V8 Developments flywheel, something I'd been meaning to do for ages
Admittedly my scales aren't the most sophisticated in the world but I did check them against a dumbbell of a known weight and they do actually prove themselves to be spot on. While the scale marks go up in one pound increments and the needle sits between the 22lb and 23lb mark it is a fraction over the half way point.
I conclude my V8 Developments lightened flywheel is approximately 10.3kg which equates to 22.7lbs, to avoid debate I'm happy to er on the side of pessimism and call it a 23lb flywheel.
A standard 4.0 litre flywheel must therefore be 30lbs as V8 Developments confirmed they took 7lbs out of mine to give me their 23lb lightened version, I can also assure you once fitted it made a big improvement to the way the engine picked up revs with absolutely no drivability downsides.
It's also been proven the very rare 5.0 litre flywheel used by TVR weighs in at 8.8kg which is 19.4lbs, so my V8 Developments lightened flywheel is significantly lighter than standard one used in the 4.0 litre cars and only just over 3lbs heavier than the specially cast 5.0 litre TVR one.
If you've been following this post you'll know I was cautious not to go too light, both people I spoke to separately who have the 15lb steel flywheel available off the shelf from V8 Tuner said they do need to raise the revs slightly more than normal when pulling away from a junction, I didn't want this so I had a bespoke all steel 8.5kg flywheel made which equates to 18.74lbs.
So what I have now is fractionally lighter than the elusive 5.0 litre flywheel and I would also imagine it to be much stronger being chromo steel rather than cast iron. Essentially I've gone from the ridiculous 30lb millstone fitted to 4.0 litre Chimaeras down to the massively better V8 Developments lighted one at a shade under 23lbs, I've then cut the weight still further by over 4lbs from there to give me an 18.74lbs flywheel with still no negative impact on dravability.
I wouldn't want to go any lighter and it has to be said the steel flywheel wasn't exactly cheap, so my conclusion is a V8 Developments lightened flywheel at a shade under 23lbs offers by far the best bang for your buck. Indeed anyone changing the clutch on their 4.0 litre car is well advised to fit one of these V8 Developments lighted flywheels because they'll definitely feel the difference without sacrificing any drivability.
Best of all a V8 Developments lightened to 23lb flywheel won't break the bank, mine currently sits redundant in my garage acting as a static reminder to the significant benefits of reducing the engine mass of a 4.0 litre Chimaera
Hope this helps people?
Dave.
This morning I popped out to the garage and weighed my V8 Developments flywheel, something I'd been meaning to do for ages
Admittedly my scales aren't the most sophisticated in the world but I did check them against a dumbbell of a known weight and they do actually prove themselves to be spot on. While the scale marks go up in one pound increments and the needle sits between the 22lb and 23lb mark it is a fraction over the half way point.
I conclude my V8 Developments lightened flywheel is approximately 10.3kg which equates to 22.7lbs, to avoid debate I'm happy to er on the side of pessimism and call it a 23lb flywheel.
A standard 4.0 litre flywheel must therefore be 30lbs as V8 Developments confirmed they took 7lbs out of mine to give me their 23lb lightened version, I can also assure you once fitted it made a big improvement to the way the engine picked up revs with absolutely no drivability downsides.
It's also been proven the very rare 5.0 litre flywheel used by TVR weighs in at 8.8kg which is 19.4lbs, so my V8 Developments lightened flywheel is significantly lighter than standard one used in the 4.0 litre cars and only just over 3lbs heavier than the specially cast 5.0 litre TVR one.
If you've been following this post you'll know I was cautious not to go too light, both people I spoke to separately who have the 15lb steel flywheel available off the shelf from V8 Tuner said they do need to raise the revs slightly more than normal when pulling away from a junction, I didn't want this so I had a bespoke all steel 8.5kg flywheel made which equates to 18.74lbs.
So what I have now is fractionally lighter than the elusive 5.0 litre flywheel and I would also imagine it to be much stronger being chromo steel rather than cast iron. Essentially I've gone from the ridiculous 30lb millstone fitted to 4.0 litre Chimaeras down to the massively better V8 Developments lighted one at a shade under 23lbs, I've then cut the weight still further by over 4lbs from there to give me an 18.74lbs flywheel with still no negative impact on dravability.
I wouldn't want to go any lighter and it has to be said the steel flywheel wasn't exactly cheap, so my conclusion is a V8 Developments lightened flywheel at a shade under 23lbs offers by far the best bang for your buck. Indeed anyone changing the clutch on their 4.0 litre car is well advised to fit one of these V8 Developments lighted flywheels because they'll definitely feel the difference without sacrificing any drivability.
Best of all a V8 Developments lightened to 23lb flywheel won't break the bank, mine currently sits redundant in my garage acting as a static reminder to the significant benefits of reducing the engine mass of a 4.0 litre Chimaera
Hope this helps people?
Dave.
So, best part of 4 years later, I am considering the same thing. Am changing the clutch in the next few weeks, and a lighter flywheel to improve response seems like a no-brainer. Pretty certain my std 400 has the original millstone fitted. All opinions welcome. car use is just fun road/touring and occasional novice track day. 20 Lbs / 9kg seems to be the optimum figure, most of the more expensive steel items seem to be more like 15Lb / 7kg. Is that too light for a boggo 4 litre?
mateypeeps1 said:
So, best part of 4 years later, I am considering the same thing. Am changing the clutch in the next few weeks, and a lighter flywheel to improve response seems like a no-brainer. Pretty certain my std 400 has the original millstone fitted. All opinions welcome. car use is just fun road/touring and occasional novice track day. 20 Lbs / 9kg seems to be the optimum figure, most of the more expensive steel items seem to be more like 15Lb / 7kg. Is that too light for a boggo 4 litre?
I'm running 18lbs now, its a custom flywheel I had TTV Racing grind for me from chro-mo billet steel.http://ttvracing.com/
I've very happy with it, but I think I could sill go lighter.
TTV are the UK flywheel experts, don't mess about with anyone else, TTV will sort you out.
The benefits of a lightened flywheel are many and varied.
Especially, as has already been mentioned the existing specification isn’t ideal for a sporting Chim.
A word of caution though, if you’re planning to have your existing flywheel lightened - ONLY take it to a specialist!
I have heard stories of flywheels lightened on a lathe and then turning into a cutting disc at 6000 rpm.
You can guess the results - an alli bellhousing wont offer much resistance........
Especially, as has already been mentioned the existing specification isn’t ideal for a sporting Chim.
A word of caution though, if you’re planning to have your existing flywheel lightened - ONLY take it to a specialist!
I have heard stories of flywheels lightened on a lathe and then turning into a cutting disc at 6000 rpm.
You can guess the results - an alli bellhousing wont offer much resistance........
More on lightened flywheels here.....
https://www.pistonheads.com/gassing/topic.asp?h=0&...
And these are the facts
For safety V8 Developments will not go any lighter than 22lbs on a standard cast flywheel, this is however already a huge improvement on the 28lb millstone you got in all Chimaeras except of course the five litre cars, the 5.0 ran a bespoke cast 20lbs flywheel.
I ran one of V8D's lightened standard cast flywheels for years which weighed in at 22.5lbs, this made a massive difference and the results were only positives, some time later I sold that flywheel to a fellow PHer for £120. I put the money towards my lighter £336.00 TTV racing steel flywheel I had TTV spin down to 18.74lbs (8.5kg) so it effectively cost me £216.00, it's now over 9lbs lighter that what the car left the factory with in 1996.
For the record 9lbs is the weight of your average sledge hammer, and a weight loss of one third over the original. However, I now think I could have gone lighter still, I currently have what I believe to be a leaky rear main seal which could mean the box will have to come out yet again, if I'm proved correct my steel flywheel will go off to TTV and get spun down to 16lbs making it a whopping 12lbs lighter than the original, a weight loss of 43% over the original so getting on for half the weight!
One thing is without question, any weight you can get out of that original ridiculously heavy 28lb original millstone is a good thing, and there's a long long way to go before you ever reach the point where drivability is affected. Keep in mind the curb weight of a Chimaera is a third lighter than that of the Rover SD1, and is why my TTV racing flywheel hasn't affected the drivability of my Chimaera at all.
The only difference you'll feel is vastly better throttle response, and on the lazy revving old Rover V8 anything you can do to help the lump spin up a bit faster is a significant positive!!!!!
Especially in a 1060kg sports car
Basically its a no-brainer
https://www.pistonheads.com/gassing/topic.asp?h=0&...
And these are the facts
| Rover SD1 | 32lbs |
| Standard cast 400/450 Chimaera | 28lbs |
| V8 Developments lightened standard cast | 23lbs |
| Bespoke TVR cast 5.0 litre | 20lbs |
| My final TTV chro/mo steel | 18.74Lbs |
| TTV stock RV8 light weight chro/mo steel | 14.55Lbs |
| TTV RV8 race spec chro/mo steel | 7.5Lbs |
For safety V8 Developments will not go any lighter than 22lbs on a standard cast flywheel, this is however already a huge improvement on the 28lb millstone you got in all Chimaeras except of course the five litre cars, the 5.0 ran a bespoke cast 20lbs flywheel.
I ran one of V8D's lightened standard cast flywheels for years which weighed in at 22.5lbs, this made a massive difference and the results were only positives, some time later I sold that flywheel to a fellow PHer for £120. I put the money towards my lighter £336.00 TTV racing steel flywheel I had TTV spin down to 18.74lbs (8.5kg) so it effectively cost me £216.00, it's now over 9lbs lighter that what the car left the factory with in 1996.
For the record 9lbs is the weight of your average sledge hammer, and a weight loss of one third over the original. However, I now think I could have gone lighter still, I currently have what I believe to be a leaky rear main seal which could mean the box will have to come out yet again, if I'm proved correct my steel flywheel will go off to TTV and get spun down to 16lbs making it a whopping 12lbs lighter than the original, a weight loss of 43% over the original so getting on for half the weight!
One thing is without question, any weight you can get out of that original ridiculously heavy 28lb original millstone is a good thing, and there's a long long way to go before you ever reach the point where drivability is affected. Keep in mind the curb weight of a Chimaera is a third lighter than that of the Rover SD1, and is why my TTV racing flywheel hasn't affected the drivability of my Chimaera at all.
The only difference you'll feel is vastly better throttle response, and on the lazy revving old Rover V8 anything you can do to help the lump spin up a bit faster is a significant positive!!!!!
Especially in a 1060kg sports car
Basically its a no-brainer
spitfire4v8 said:
I alluded to this in one of the previous threads on light flywheels .. with 4 firing pulses per rev, and a heavy crank, I don't know why people just don't go for a very light flywheel
I'm inclined to agree, but how light is 'very light' Joolz 
My current thinking is I could have just jumped to 16lbs with no ill effects
Your thoughts and experiences are welcomed
Plenty of people running 5kg flywheels on 4cylinder fords, with less crank mass and half the firing events per rev .. so I would have thought 5kg/11lbs would be fine, BUT of course we have a big diameter so whether you can get to those numbers without the special race flywheels costing a fortune I don't know .. but it would seem that significantly lighter than what you have now should be possible.
Remember we have relatively low compression engines, and a firing pulse / crank pin angles turning the crank every 90 degrees of rotation, and a heavier crank than a little 4pot engine would have.
It all adds up to our engines being able to take a much lighter flywheel compared to a 4 pot..
The TTV light flywheel for the Cerbera is 3.4kg !!
Remember we have relatively low compression engines, and a firing pulse / crank pin angles turning the crank every 90 degrees of rotation, and a heavier crank than a little 4pot engine would have.
It all adds up to our engines being able to take a much lighter flywheel compared to a 4 pot..
The TTV light flywheel for the Cerbera is 3.4kg !!
spitfire4v8 said:
Plenty of people running 5kg flywheels on 4cylinder fords, with less crank mass and half the firing events per rev .. so I would have thought 5kg/11lbs would be fine, BUT of course we have a big diameter so whether you can get to those numbers without the special race flywheels costing a fortune I don't know .. but it would seem that significantly lighter than what you have now should be possible.
Remember we have relatively low compression engines, and a firing pulse / crank pin angles turning the crank every 90 degrees of rotation, and a heavier crank than a little 4pot engine would have.
It all adds up to our engines being able to take a much lighter flywheel compared to a 4 pot..
The TTV light flywheel for the Cerbera is 3.4kg !!
Wow, 3.4kg! Now that is light Remember we have relatively low compression engines, and a firing pulse / crank pin angles turning the crank every 90 degrees of rotation, and a heavier crank than a little 4pot engine would have.
It all adds up to our engines being able to take a much lighter flywheel compared to a 4 pot..
The TTV light flywheel for the Cerbera is 3.4kg !!
Alan Crisp of TTV once told me its not so much the overall weight of the flywheel that counts, its where the flywheel caries that weight, this made sense to me. Basically what he was saying was if you take two flywheels of the same weight but one of them has most of the mass in the centre and the other caries most of its mass on the outer ring gear edge, despite both flywheels weighing exactly the same the one with the mass in the centre will alow the engine to spin up faster.
The lighter you can make the outer ring gear edge of the flywheel the faster the engine will spin up, you can see this in the following RV8 flywheel from V8 Tuner which almost certainly is made by TTV Racing (£420) but V8 Tuner doesn't state how much it weighs, when you go on the TTV website you see what appears to me the same flywheel described as being 3.4 Kg (7.5lbs).
This is however described by V8 Tuner as a 'Competition Flywheel' so maybe a step too far for the road, didn't Engineer1949 fit this flywheel to the orange supercharged Chimaera, but promptly removed it as it was found to be too light
V8 Tuner also offers what they call their Rover V8 Super Lightweight Steel Flywheel which they say is approximately 6.85kg (15lbs), again this flywheel almost certainly comes from TTV, if you go on the TTV site you'll find this one they state is 6.6kg (14.55 lbs)
http://ttvracing.com/product/rover-v8-lite-for-9-5...
I think I'll have Alan Crisp spin down my 18.74 lbs TTV Racing flywheel to 14.55 lbs and let him choose where to take the weight out as he clearly knows his stuff, I suspect most of the weight will come out of the outer ring gear edge, one thing is for sure each time I go lighter the more I like the results, and as yet I've suffered absolutely no drivability issues in the process.
| Rover SD1 | 32lbs |
| Standard cast 400/450 Chimaera | 28lbs |
| V8 Developments lightened standard cast | 23lbs |
| Bespoke TVR cast 5.0 litre | 20lbs |
| My final TTV chro/mo steel | 18.74Lbs |
| TTV stock RV8 light weight chro/mo steel | 14.55Lbs |
| TTV RV8 race spec chro/mo steel | 7.5Lbs |
That beautiful competition flywheel also has a friction surface for a small multiplate clutch, which further decreases the effective inertia, but also forces you into a more on-off clutch action because the smaller the mean effective radius of a clutch (or brake disc) the more chance it has of grabbing when engaging or when a brake disc is close to locking-up.
You might want to run a full diameter clutch to avoid this and give a progressive action.
It would be interesting to hear why people think a particular flywheel might be "too light .." just saying those words isn't particularly helpful to anyone else without some kind of description to go along with them.
You might want to run a full diameter clutch to avoid this and give a progressive action.
It would be interesting to hear why people think a particular flywheel might be "too light .." just saying those words isn't particularly helpful to anyone else without some kind of description to go along with them.
I ran a rally car for many years before I ventured into TVR ownership, so understand something of the benefit of lightened flywheels.
In a competition scenario (more so on the track, than on a rally stage), a very light flywheel will benefit because in race competition you generally maintain the engine at higher revs I.e a narrower top end of the Rev band - where a competition engine develops most of its power.
As such, the low inertia of a very light flywheel allows the engine to “spool” up very quickly.
This won’t work in a road car because you don’t maintain the engine at high revs most of the time and once you’re “off the gas”, a flywheel that is too light will cause the engine to lose revs too quickly, as the inertia is lost - it’s what’s caused the “flywheel effect”.
Ultimately, the standard flywheel in a Chim 400 etc is too heavy.
It’s suited to a Range Rover, not a sports car.
So, you want it the engine to spool up quicker than a mud plugger.
But, at the same time, you don’t want it too light, or road drive ability will be lost with off gas revs dropping too quickly.
In a competition scenario (more so on the track, than on a rally stage), a very light flywheel will benefit because in race competition you generally maintain the engine at higher revs I.e a narrower top end of the Rev band - where a competition engine develops most of its power.
As such, the low inertia of a very light flywheel allows the engine to “spool” up very quickly.
This won’t work in a road car because you don’t maintain the engine at high revs most of the time and once you’re “off the gas”, a flywheel that is too light will cause the engine to lose revs too quickly, as the inertia is lost - it’s what’s caused the “flywheel effect”.
Ultimately, the standard flywheel in a Chim 400 etc is too heavy.
It’s suited to a Range Rover, not a sports car.
So, you want it the engine to spool up quicker than a mud plugger.
But, at the same time, you don’t want it too light, or road drive ability will be lost with off gas revs dropping too quickly.
Do remember however the stock TVR fitted FW is not a Defender/Range Rover unit its a Rover SD1 unit hence why we use a 9.5" clutch and not the LR/RR 10.5" assy , if you have ever driven bike powered vehicles you'll get a feel for how too much low inertia affects pulling away and low speed driveabilty , my advice is dont over do things otherwise you will have a ON/OFF switch feel as mentioned above which kinda defeats the idea of a V8 for many 
which kinda defeats the idea of a V8 for many Bloke, haven't read all posts, life's short now at my age so apologies 
Anyway, for what it's worth, Go Steel, go Light (but not overly and from memory mine was 19lb) and have EVERYTHING balanced, the complete assembly and don't skimp on few quid whilst you're going for it. Good luck. 
Anyway, for what it's worth, Go Steel, go Light (but not overly and from memory mine was 19lb) and have EVERYTHING balanced, the complete assembly and don't skimp on few quid whilst you're going for it. Good luck. Edited by macdeb on Monday 1st June 17:04
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