Lightened flywheel
Discussion
Hi Alun, I've been through all this twice.
STEP 1
Began with the need for a new clutch, at which point I discovered my standard cast flywheel weighed a comically heavy 28lb, I discussed this with V8 Developments who supplied a Helix clutch (which was the wrong choice). V8D were able to supply me with an exchange unit machined down to 23lb, as you can imagine removing a full 5lbs made a massive difference, the engine span up noticeably quicker and throttle response was greatly enhanced.
Best of all the engine remained smooth and tractable and this on a Stealth cam, within the first 50 miles it was very clear to me there were absolutely disadvantages in taking 18% of mass out the original millstone. Rob at V8D confirmed the flywheel fitted by TVR to my 1996 4.0HC was the same as fitted to a 4.5 Chimaera, they are all the 28Lb unit which is definitely unnecessarily heavy.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
STEP 2
Given how well step one went when I'd finally had enough of living with the excessively heavy Helix clutch I decided to explore the idea of going lighter still, the first thing I found out was that on the grounds of safety V8D were not prepared to take a cast flywheel lower than the 23lbs they'd already given me, they advised further benefits were available in going lighter but it just wasn't safe to machine a cast RV8 flywheel any further.
TVR knew all this themselves, looking to address the lazy nature of their stroked 5.0 litre engine they commissioned their own lightened flywheel casting which weighs 20lb, this unit is only found in Chimaeras and Griffiths fitted with the 5.0 litre engine and I soon discovered sourcing one was impossible as they're as rare as hen's teeth.
The bespoke TVR 5.0 litre casting looks different to the Rover SD1 type used in the 4.0 and 4.5 litre Chimaeras, it has a kind of spoked arrangement as shown here...
The solution was to move on from cast and go to a steel flywheel, I discussed my requirements with TTV Racing who are the go-to UK specialists for all steel bespoke machined flywheels, they already offer a 14.55lb steel flywheel for the RV8 but I was concerned this could be a step too far as I do very much value smooth drivabilty in town. What we ended up going for weighs exactly 8.5kg which is 18.74Lbs making it a further 4.26lbs lighter than my V8 Developments lightened cast unit and more or less a full 10lbs lighter than my original..... which is a huge weight reduction of 35%!
My TTV Racing bespoke steel 18.74Lbs flywheel took throttle response to the next level and I love it, I can honestly say there are absolutely no disadvantages... just further benefits
Here's how the RV8 flywheel options weigh in, although it has to be said TTV Racing will give you whatever you want.
I'd wager the TTV race spec 7.5lb flywheel is going to be a massive step too far for the road, their 14.55lb unit is probably fine but at the end of the day fitting a flywheel isn't a 10 minute job so I decided to play it safe by going with a bespoke 18.74lbs unit which is just over a pound lighter than the TVR 5.0 litre unit but being steel is way stronger.
In conclude if you're having a new clutch fitted or you are completing a body off chassis restoration fitting a lightened flywheel is an absolute no-brainer, you will notice a big positive improvement in throttle response and the engine's ability to pick up RPMs, but be careful how light you go because if you go too far and find you've lost drivability it's an expensive job to resolve.
However despite all my figures you actually can't go by weight because with flywheels its not the overall mass on the scales that counts its where the mass sits on the flywheel, leave the majority of the mass at the centre of the flywheel and a very heavy flywheel will behave like a much lighter one, machine a very light flywheel but leave most of its mass on the outer ring gear edge and it'll feel like a far heavier unit.
My final point is all this is subjective, by that I mean one man's too light is another man's too heavy, everyone has different expectations for how their TVR should drive. I'm obsessed with ensuring my Chimaera drives super smoothly through town with lovely gear changes, but I do still want the car to feel as bright on the throttle as I can possibly make it without compromising drivability. What I can tell you is my 4.0HC is way way smoother than it was when it ran a 28lb flywheel and the Kent 435 cam despite me going to an 18.75lb flywheel and a Stealth performance cam, this has a lot to do with running an aftermarket engine management system so what I've been able to achieve is an engine that spins up much much faster yet is actually smoother that it was from new.
Its a win win
STEP 1
Began with the need for a new clutch, at which point I discovered my standard cast flywheel weighed a comically heavy 28lb, I discussed this with V8 Developments who supplied a Helix clutch (which was the wrong choice). V8D were able to supply me with an exchange unit machined down to 23lb, as you can imagine removing a full 5lbs made a massive difference, the engine span up noticeably quicker and throttle response was greatly enhanced.
Best of all the engine remained smooth and tractable and this on a Stealth cam, within the first 50 miles it was very clear to me there were absolutely disadvantages in taking 18% of mass out the original millstone. Rob at V8D confirmed the flywheel fitted by TVR to my 1996 4.0HC was the same as fitted to a 4.5 Chimaera, they are all the 28Lb unit which is definitely unnecessarily heavy.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
STEP 2
Given how well step one went when I'd finally had enough of living with the excessively heavy Helix clutch I decided to explore the idea of going lighter still, the first thing I found out was that on the grounds of safety V8D were not prepared to take a cast flywheel lower than the 23lbs they'd already given me, they advised further benefits were available in going lighter but it just wasn't safe to machine a cast RV8 flywheel any further.
TVR knew all this themselves, looking to address the lazy nature of their stroked 5.0 litre engine they commissioned their own lightened flywheel casting which weighs 20lb, this unit is only found in Chimaeras and Griffiths fitted with the 5.0 litre engine and I soon discovered sourcing one was impossible as they're as rare as hen's teeth.
The bespoke TVR 5.0 litre casting looks different to the Rover SD1 type used in the 4.0 and 4.5 litre Chimaeras, it has a kind of spoked arrangement as shown here...
The solution was to move on from cast and go to a steel flywheel, I discussed my requirements with TTV Racing who are the go-to UK specialists for all steel bespoke machined flywheels, they already offer a 14.55lb steel flywheel for the RV8 but I was concerned this could be a step too far as I do very much value smooth drivabilty in town. What we ended up going for weighs exactly 8.5kg which is 18.74Lbs making it a further 4.26lbs lighter than my V8 Developments lightened cast unit and more or less a full 10lbs lighter than my original..... which is a huge weight reduction of 35%!
My TTV Racing bespoke steel 18.74Lbs flywheel took throttle response to the next level and I love it, I can honestly say there are absolutely no disadvantages... just further benefits
Here's how the RV8 flywheel options weigh in, although it has to be said TTV Racing will give you whatever you want.
| 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 |
I'd wager the TTV race spec 7.5lb flywheel is going to be a massive step too far for the road, their 14.55lb unit is probably fine but at the end of the day fitting a flywheel isn't a 10 minute job so I decided to play it safe by going with a bespoke 18.74lbs unit which is just over a pound lighter than the TVR 5.0 litre unit but being steel is way stronger.
In conclude if you're having a new clutch fitted or you are completing a body off chassis restoration fitting a lightened flywheel is an absolute no-brainer, you will notice a big positive improvement in throttle response and the engine's ability to pick up RPMs, but be careful how light you go because if you go too far and find you've lost drivability it's an expensive job to resolve.
However despite all my figures you actually can't go by weight because with flywheels its not the overall mass on the scales that counts its where the mass sits on the flywheel, leave the majority of the mass at the centre of the flywheel and a very heavy flywheel will behave like a much lighter one, machine a very light flywheel but leave most of its mass on the outer ring gear edge and it'll feel like a far heavier unit.
My final point is all this is subjective, by that I mean one man's too light is another man's too heavy, everyone has different expectations for how their TVR should drive. I'm obsessed with ensuring my Chimaera drives super smoothly through town with lovely gear changes, but I do still want the car to feel as bright on the throttle as I can possibly make it without compromising drivability. What I can tell you is my 4.0HC is way way smoother than it was when it ran a 28lb flywheel and the Kent 435 cam despite me going to an 18.75lb flywheel and a Stealth performance cam, this has a lot to do with running an aftermarket engine management system so what I've been able to achieve is an engine that spins up much much faster yet is actually smoother that it was from new.
Its a win win
macdeb said:
Had one on mine, went 'Steel' over concerns of the above 
Good call Mac 
there is a risk with cast FW's and you need to know what your doing hence why I had my cast one done at JE then decided during build I would go lighter still and this meant steel was the only option and glad I did , Alun seeing as you like a well behaved and smooth low down delivery I think COG/Daves solution could well be for you cake and eat it kinda thing 
failing that you could look for an elusive 500 FW but then thats still cast iron, and like I say you will still need to talk to Powers concerning how your motor was balanced and if its a Yea or Nay Edited by Zener on Thursday 30th January 09:28
Classic Chim said:
Thanks for all this useful advice lads.
So do I need a special puller to remove my old one?
So steel is the way to go. Ok.
Nope no puller needed, I would however renew the FW bolts no chancing with this kind of thing but thats just me I went ARP available and cheap from Realsteel the steel FW is an interference fit on the crank raised spigot bearing housing/Tit So do I need a special puller to remove my old one?
So steel is the way to go. Ok.
this is a feature of this kind of unit and in the literature anyways just thought i'd mention Edited by Zener on Thursday 30th January 09:44
Zener said:
ope no puller needed, I would however renew the FW bolts but thats just me I went ARP available and cheap from Realsteel the steel FW is an interference fit on the crank raised spigot bearing housing/Tit this is a feature of this kind of unit and in the literature anyways just though i'd mention
this is a feature of this kind of unit and in the literature anyways just though i'd mention Zener said:
Where you remove material as everything to do with keeping the FW's integrity/strength ultimately & above all else especially with a cast iron FW
exaclty right - i mentioned that the mounting holes were in the middle in my previous post, often people take weight frim the middle and wonder why it no longer has the material strneght to stay in one piece. if youre not familir with lathes and loadings and rotational inertia its probably best to pay someone with experience. especially with a cast iron FW Mart at Gas n Gears is my go-to guy for drivetrain stuff
Edited by Olas on Thursday 30th January 12:28
Do consider your 4.5 will make more torque than my 4.0 Alun which means you may be able to go lighter than I did, after much deliberation and some largely unscientific calculations I settled on 18.75lbs which proved itself to work great for me, but the truth is I chickened out of going any lighter and played it safe.
I've have heard tale 16lbs is the sweet spot but as I've said already it's not the overall weight but where the weight sits on flywheel that makes the biggest difference, you then have to be honest with yourself about what you see as acceptable in the way of drivability, finally you'll inevitably need to take a punt, there are so many variables you just can't say the ideal will be one weight or another.
However what I can tell you with 100% confidence is:
1. The 28lb flywheel you currently have is way heavier than it needs to be
2. TVR themselves went down to 20lbs on the 5.0 litre for good reason
3. The TVR 5.0 flywheel is still cast and finding one is not going to be easy
4. Don't be tempted to machine down your stock 28lb flywheel much past 23lbs or it'll become unsafe, less than this and you'll need to switch to steel
5. A standard 28lb flywheel machined down to 23lbs is a great mod for very little money, it stands next to a full de-cat as the best bang for buck for any Chimaera, this followed by a cam change. Complete a full de-cat, fit a decent fresh performance cam like the Stealth from V8D then get that 28lb millstone down to 23lbs and the engine is transformed, top it all off with an aftermarket engine management system and suddenly the old 4X4 lump finally feels like a sports car engine
6. My 18.75lbs steel flywheel from TTV is proven to work even better than 23lbs with no down sides, I expect you'd be happy with the same
7. TTV Racing make a good steel RV8 flywheel and have the knowledge to give you what you want
8. You can remove weight from a flywheel but you can't add it back on, if you find you've gone too light the only solution is to start again with a new flywheel
9. Check with your engine builder before doing anything flywheel related
If Dom gives you the green light, as the very minimum I strongly recommend fitting a standard flywheel machined down to 23lbs, it won't have any negative effects on drivability but saying that it won't give you any more true horsepower either.
However, it absolutely will feel like you've added at least 10hp especially when pulling away!
https://www.pistonheads.com/gassing/topic.asp?h=0&...
I've have heard tale 16lbs is the sweet spot but as I've said already it's not the overall weight but where the weight sits on flywheel that makes the biggest difference, you then have to be honest with yourself about what you see as acceptable in the way of drivability, finally you'll inevitably need to take a punt, there are so many variables you just can't say the ideal will be one weight or another.
However what I can tell you with 100% confidence is:
1. The 28lb flywheel you currently have is way heavier than it needs to be
2. TVR themselves went down to 20lbs on the 5.0 litre for good reason
3. The TVR 5.0 flywheel is still cast and finding one is not going to be easy
4. Don't be tempted to machine down your stock 28lb flywheel much past 23lbs or it'll become unsafe, less than this and you'll need to switch to steel
5. A standard 28lb flywheel machined down to 23lbs is a great mod for very little money, it stands next to a full de-cat as the best bang for buck for any Chimaera, this followed by a cam change. Complete a full de-cat, fit a decent fresh performance cam like the Stealth from V8D then get that 28lb millstone down to 23lbs and the engine is transformed, top it all off with an aftermarket engine management system and suddenly the old 4X4 lump finally feels like a sports car engine
6. My 18.75lbs steel flywheel from TTV is proven to work even better than 23lbs with no down sides, I expect you'd be happy with the same
7. TTV Racing make a good steel RV8 flywheel and have the knowledge to give you what you want
8. You can remove weight from a flywheel but you can't add it back on, if you find you've gone too light the only solution is to start again with a new flywheel
9. Check with your engine builder before doing anything flywheel related
If Dom gives you the green light, as the very minimum I strongly recommend fitting a standard flywheel machined down to 23lbs, it won't have any negative effects on drivability but saying that it won't give you any more true horsepower either.
However, it absolutely will feel like you've added at least 10hp especially when pulling away!
https://www.pistonheads.com/gassing/topic.asp?h=0&...
So on the RV8 it has two end weights,
1 the front pulley
2 flywheel +clutch.
My front pulley wheel is balanced as is my flywheel.
A known reputable lightened flywheel will be balanced too I assume so this should not effect my cranks balance.
I don’t want to knock out what is a new bottom end on my car. A lightened flywheel must surely be centre balanced when made so should be ok to use.
Does this sound correct.
Can someone calculate the gains achieved over a 1/4 mile using a 8.5 kg one roughly from the standard 14 or possibly 16 kg as I don’t know what mine weighs
If it’s like 3/10th of a second it’s getting done
I’ve had the go ahead boys,,,,,,,, : thumbup:
Trouble is another mod that will knock 1k off the sale price come the day,,, 3/10ths though that’s like the holy grail to me
1 the front pulley
2 flywheel +clutch.
My front pulley wheel is balanced as is my flywheel.
A known reputable lightened flywheel will be balanced too I assume so this should not effect my cranks balance.
I don’t want to knock out what is a new bottom end on my car. A lightened flywheel must surely be centre balanced when made so should be ok to use.
Does this sound correct.
Can someone calculate the gains achieved over a 1/4 mile using a 8.5 kg one roughly from the standard 14 or possibly 16 kg as I don’t know what mine weighs
If it’s like 3/10th of a second it’s getting done
I’ve had the go ahead boys,,,,,,,, : thumbup:
Trouble is another mod that will knock 1k off the sale price come the day,,, 3/10ths though that’s like the holy grail to me
Edited by Classic Chim on Thursday 30th January 13:50
In an ideal world the engine will be internally balanced and the flywheel and damper will be neutral balance. This means they can be swopped for other neutral balanced parts without upsetting the engine. Same goes for clutch packs I imagine.
On some engines (ls vettes) there will be some additional fine balancing of the damper and flywheel which contributes to an extra 500 rpm's. The camaro's don't have this luxury. :-)
On some engines (ls vettes) there will be some additional fine balancing of the damper and flywheel which contributes to an extra 500 rpm's. The camaro's don't have this luxury. :-)
Boosted LS1 said:
In an ideal world the engine will be internally balanced and the flywheel and damper will be neutral balance. This means they can be swopped for other neutral balanced parts without upsetting the engine. Same goes for clutch packs I imagine.
On some engines (ls vettes) there will be some additional fine balancing of the damper and flywheel which contributes to an extra 500 rpm's. The camaro's don't have this luxury. :-)
I watched an old time video of Jaguar production once, cranks being balanced so would the RV ones be balanced as an individual item long before it went in an engine. On some engines (ls vettes) there will be some additional fine balancing of the damper and flywheel which contributes to an extra 500 rpm's. The camaro's don't have this luxury. :-)
If so as long as I get a balanced flywheel I should’nt have any problems, shucks MAC had one so it must be right
Classic Chim said:
So on the RV8 it has two end weights,
1 the front pulley
2 flywheel +clutch.
My front pulley wheel is balanced as is my flywheel.
A known reputable lightened flywheel will be balanced too I assume so this should not effect my cranks balance.
I don’t want to knock out what is a new bottom end on my car. A lightened flywheel must surely be centre balanced when made so should be ok to use.
Does this sound correct.
1 the front pulley
2 flywheel +clutch.
My front pulley wheel is balanced as is my flywheel.
A known reputable lightened flywheel will be balanced too I assume so this should not effect my cranks balance.
I don’t want to knock out what is a new bottom end on my car. A lightened flywheel must surely be centre balanced when made so should be ok to use.
Does this sound correct.
No it doesn't, I'm afraid...
CHECK WITH DOM - I was looking at doing this a few years ago, engine rebuilt by Dom just like yours....
Entire rotating assembly had been balanced by Dom as a single piece - so simply switching the FW over would throw the whole thing out of balance, with disastrous consequences...
If Dom did it the same as mine, you will need to take it the FW/crank /pulley combo from the block, change the FW and get the whole thing rebalanced - then reinstall. Big money.
Also, doesn't look like anyone's mentioned that a lighter flywheel will increase engine braking - for what it's worth...
HTH,
Dom
Classic Chim said:
Boosted LS1 said:
In an ideal world the engine will be internally balanced and the flywheel and damper will be neutral balance. This means they can be swopped for other neutral balanced parts without upsetting the engine. Same goes for clutch packs I imagine.
On some engines (ls vettes) there will be some additional fine balancing of the damper and flywheel which contributes to an extra 500 rpm's. The camaro's don't have this luxury. :-)
I watched an old time video of Jaguar production once, cranks being balanced so would the RV ones be balanced as an individual item long before it went in an engine. On some engines (ls vettes) there will be some additional fine balancing of the damper and flywheel which contributes to an extra 500 rpm's. The camaro's don't have this luxury. :-)
If so as long as I get a balanced flywheel I should’nt have any problems, shucks MAC had one so it must be right
Dominic TVRetto said:
No it doesn't, I'm afraid...
CHECK WITH DOM - I was looking at doing this a few years ago, engine rebuilt by Dom just like yours....
Entire rotating assembly had been balanced by Dom as a single piece - so simply switching the FW over would throw the whole thing out of balance, with disastrous consequences...
If Dom did it the same as mine, you will need to take it the FW/crank /pulley combo from the block, change the FW and get the whole thing rebalanced - then reinstall. Big money.
Also, doesn't look like anyone's mentioned that a lighter flywheel will increase engine braking - for what it's worth...
HTH,
Dom
He’s often put me off the idea? CHECK WITH DOM - I was looking at doing this a few years ago, engine rebuilt by Dom just like yours....
Entire rotating assembly had been balanced by Dom as a single piece - so simply switching the FW over would throw the whole thing out of balance, with disastrous consequences...
If Dom did it the same as mine, you will need to take it the FW/crank /pulley combo from the block, change the FW and get the whole thing rebalanced - then reinstall. Big money.
Also, doesn't look like anyone's mentioned that a lighter flywheel will increase engine braking - for what it's worth...
HTH,
Dom
There’s no question the engine vibrates less at high revs than it did before he rebuilt it or that’s always been my perception at least.
I’m not sure what I’d gain in the real world as I’m a plodder on the roads.
Don’t get involved with boy racers so other than a few Hp gain a bit like my baffled sump, nice to have but somewhat pointless.
Any thoughts on this from guys with rebuilt engines who just put a lightened flywheel on.
phazed said:
Never noticed any increase in engine braking although if it's marginal I wouldn't have noticed it.
I have heard of people who lock up the rears when changing down, more engine braking compared to a 4 pot. I always heal and toe so have never had a problem.
Well this is another thing,,, I have a lot of engine breaking, I’d lock wheels everytime without blipping the throttle,,, I have heard of people who lock up the rears when changing down, more engine braking compared to a 4 pot. I always heal and toe so have never had a problem.
Not sure what to make of all of this. Surely a flywheel needs to be balanced as part of the complete thing or is it the case of if the flywheel has been centrifugally balanced it’s ok to fit.
If I do this I want John Eales to do it as it keeps it all close to home.
Ill make more calls
Boosted LS1 said:
phazed said:
Yes, aluminium flywheels (steel inserts) seem to work and even better with smaller multi plate clutches. The flywheel's then only there to support the ring gear. Top job :-)Gassing Station | Chimaera | Top of Page | What's New | My Stuff