Lightened Flywheels in a Supercharged V8.
Discussion
Ok Techies, here's one for you.
My V8 project needs a bespoke flywheel to be manufactured and it's hard to get the spec right.
For example I need one from a material that can rev potentially to 8k so believe that rules out bastardising an existing cast item. Yes?
The next point is that it's going in a lightweight (approx 1000kg - 1100kg) car so I have to be careful how light the flywheel is otherwise it could not provide enough inertia and could cause rear wheel lock up. So any ideas how I can calculate the weight in relation to diameter etc.
Then the killer question...... if I have a belt driven charger (rather than turbos) this surely has a flywheel effect because of parasitic drag at lower revs, but how would it behave at high rpm lift off? Would it actually have it's own inertia and have a run on effect therefore allowing me to take weight out of the flywheel, or the opposite??????
Help, I need a
!
Mark
My V8 project needs a bespoke flywheel to be manufactured and it's hard to get the spec right.
For example I need one from a material that can rev potentially to 8k so believe that rules out bastardising an existing cast item. Yes?
The next point is that it's going in a lightweight (approx 1000kg - 1100kg) car so I have to be careful how light the flywheel is otherwise it could not provide enough inertia and could cause rear wheel lock up. So any ideas how I can calculate the weight in relation to diameter etc.
Then the killer question...... if I have a belt driven charger (rather than turbos) this surely has a flywheel effect because of parasitic drag at lower revs, but how would it behave at high rpm lift off? Would it actually have it's own inertia and have a run on effect therefore allowing me to take weight out of the flywheel, or the opposite??????
Help, I need a
! Mark
Supercharged V8 revving to 8k, that sounds very tasty!
1000 Kgs isn't particularly light, what is the rear wheel lock-up issue you're referring to? I know people do run very high power-to-weight ratios with very low flywheel inertia without any particular problems. I would have thought the main issues with a lightened flywheel would be idle stability and the ability to pull away at low revs without stalling (especially if you have a heavy clutch?).
The blower will have some inertia (will depend on the blower type and gearing), but the drive belt will act as a torque limiter preventing the inertia from doing you any good. However it might cause problems. Depending how much you lighten the engine and hence how quickly it picks up revs, and how much torque your belt can take, you might find the inertia of the blower causes some belt slip when you blip the throttle in neutral.
1000 Kgs isn't particularly light, what is the rear wheel lock-up issue you're referring to? I know people do run very high power-to-weight ratios with very low flywheel inertia without any particular problems. I would have thought the main issues with a lightened flywheel would be idle stability and the ability to pull away at low revs without stalling (especially if you have a heavy clutch?).
The blower will have some inertia (will depend on the blower type and gearing), but the drive belt will act as a torque limiter preventing the inertia from doing you any good. However it might cause problems. Depending how much you lighten the engine and hence how quickly it picks up revs, and how much torque your belt can take, you might find the inertia of the blower causes some belt slip when you blip the throttle in neutral.
GreenV8S said:
Supercharged V8 revving to 8k, that sounds very tasty!
Only potential at the moment. If revs max at 6.5 or 7 I would still go for 8k spec as insurance, and to minimise future costs should I go mad and want more. Transmission would be the limiter.
I'm toying with a centrifugal charger of about 12 rib so it should grip the pulley.
My Cobra can lock up easily in the very wet/greay when lifting off and I've been warned about going too light on that flywheel otherwise it could happen in the dry.
So with this new project engine I don't want to get it wrong so doing my homework.
I was thinking that the parasitic drag might allow me to go lighter on the flywheel giving me quicker engine pick up.
Hmmmmmmm
M
So the issue is basically the amount of engine braking? Wouldn't have thought that flywheel inertia would make much odds in that case. It might take a fraction longer for the wheels to slow down with a heavier flywheel, but if there's more engine braking than grip they're going to slide.
Do you have fuel cut on overrun? This is something that has caught me out in the past on cold slicks. A sudden sharp increase in engine braking can be enough to upset the car and even break the tyres loose. Once they're sliding there's less grip and they keep sliding. If you disabled overun fuel cut you would get less engine braking but more important avoid this sudden jolt. If you lowered the CR to allow higher boost levels that would reduce the engine braking too?
Do you have fuel cut on overrun? This is something that has caught me out in the past on cold slicks. A sudden sharp increase in engine braking can be enough to upset the car and even break the tyres loose. Once they're sliding there's less grip and they keep sliding. If you disabled overun fuel cut you would get less engine braking but more important avoid this sudden jolt. If you lowered the CR to allow higher boost levels that would reduce the engine braking too?
I've never really understood the idle quality issue with lightweight flywheels.
What you feel in the car is the torque reaction on the flywheel of every cylinder firing .. ie as a cylinder fires it accelerates the flywheel, but it has inertia so is reluctant to accelerate so teh reaction is fed back through the engine mounts and into teh car itself. Momentum then carries to teh next cylinder firing, losing some angular velocity as it does so until accelerated again by the next cylinder. The engine goes in a series of accelerations and decelerations depending on whether it has just been given an enrgy input or it's using it up until teh next one.
However if you have a light flywheel it will accelerate on each firing much easier because it has less inertia, so less torque reaction is fed into the engine mounts and less into the car. The flywheel however has less momentum to carry it to the next firing cylinder so will lose more angular velocity, so the next cylinder fire will have to speed the flyhweel more but it's lighter so the net energy input should be roughly the same as before.
So why isn't the engine just as smooth if not smoother when the flywheel is lightened? if it's easier to accelerate by each cylinder firing it *should* impart less torque reaction into the car.
.. or something ..
What you feel in the car is the torque reaction on the flywheel of every cylinder firing .. ie as a cylinder fires it accelerates the flywheel, but it has inertia so is reluctant to accelerate so teh reaction is fed back through the engine mounts and into teh car itself. Momentum then carries to teh next cylinder firing, losing some angular velocity as it does so until accelerated again by the next cylinder. The engine goes in a series of accelerations and decelerations depending on whether it has just been given an enrgy input or it's using it up until teh next one.
However if you have a light flywheel it will accelerate on each firing much easier because it has less inertia, so less torque reaction is fed into the engine mounts and less into the car. The flywheel however has less momentum to carry it to the next firing cylinder so will lose more angular velocity, so the next cylinder fire will have to speed the flyhweel more but it's lighter so the net energy input should be roughly the same as before.
So why isn't the engine just as smooth if not smoother when the flywheel is lightened? if it's easier to accelerate by each cylinder firing it *should* impart less torque reaction into the car.
.. or something ..
I follow that, but if it *doesn't* stall, why is it rougher?
I reckon that it's partly a myth. When you lighten a flywheel you've more likely modifed the rest of the engine, higher compression, wilder cam .. in the olden days you'd have either not bothered to modify the dizzy advance, or you're running more low speed advance to help smooth out an already lumpy engine.
I put forward a managed engine these days on a light flywheel will be as smooth as with a heavy one ..
as i say the speed variation isn't the problem as long as it doesn't get too out of hand (unlikely on a V8 certainly) .. and if there's less inertia there's les torque reaction to rock the car ..
I reckon that it's partly a myth. When you lighten a flywheel you've more likely modifed the rest of the engine, higher compression, wilder cam .. in the olden days you'd have either not bothered to modify the dizzy advance, or you're running more low speed advance to help smooth out an already lumpy engine.
I put forward a managed engine these days on a light flywheel will be as smooth as with a heavy one ..
as i say the speed variation isn't the problem as long as it doesn't get too out of hand (unlikely on a V8 certainly) .. and if there's less inertia there's les torque reaction to rock the car ..
I want to understand this also as the std flywheel and clutchs (auto) on my BMW V12 is rather heavy, but similar weight to the porsche/chevy setup in my Ultima.
I have already 'saved' over 20kgs as I have a 200mm tripple plate unit..... and the flywheels normally fitted to these clutches are also extremelly light.
Also i do not have much room for a large flywheel and it would take some engineering to get some weight into it.
My engine is also forced induction (twin turbos)and destined for between 7-8000rpm (hopefully) and going in a car of around 1000kgs.
I have already 'saved' over 20kgs as I have a 200mm tripple plate unit..... and the flywheels normally fitted to these clutches are also extremelly light.
Also i do not have much room for a large flywheel and it would take some engineering to get some weight into it.
My engine is also forced induction (twin turbos)and destined for between 7-8000rpm (hopefully) and going in a car of around 1000kgs.
joospeed said:
I follow that, but if it *doesn't* stall, why is it rougher?
Is it rougher? If it is, it may well be that the spec of the engine has a large part to play, as you say. But I also wonder whether the reduced speed has some other side effects. I imagine the ignition timing would need to be retarded further, but these slow speeds would probably be off the end of any mechanical advance. EGR increases sharply as the revs drop (something that is causing me *no end* of grief at the moment), eventually this will get severe enough to cause running problems. I think typically when you have excessive EGR you get alternating 'good' and 'bad' firings where each 'good' firing contaminates the following one. This would cause the speed to be even more eratic, possibly making this sort of problem worse.
I don't know, this is all speculation, but I can see why a lighter flywheel *might* make the idle more eratic, as well as raising the stall speed.
I suppose you associate long cams with race engines, big valves and ports and REVS. I suppose a lightened flywheel added for a reduction of rotating weight gave lumpyness at low revs do to charge dilution (insufficient port velocity) and woolyness. With a blown engine, running a light flywheel should keep everythiong going in the right direction and prevent the woolyness. With a high CR, detonation causes the engine to be "clanky".
With my SC engine (rootes), I am running a lightened to the maximum flywheel. The supercharger will be enough of a drag anyway. I want my responsiveness. With a centrifugal blower, surely this is the worst of both worlds, belt driven and exponential boost characteristic? Bearing in mind, I am running light wheels and everything else which I have to accellerate.
Edit:- We are talking V8's and so I would have thought the flywheel was of only real importance for mounting the ring gear.....(Bearing in mind I am not that bothered about smoothness)
>> Edited by love machine on Saturday 22 January 14:12
With my SC engine (rootes), I am running a lightened to the maximum flywheel. The supercharger will be enough of a drag anyway. I want my responsiveness. With a centrifugal blower, surely this is the worst of both worlds, belt driven and exponential boost characteristic? Bearing in mind, I am running light wheels and everything else which I have to accellerate.
Edit:- We are talking V8's and so I would have thought the flywheel was of only real importance for mounting the ring gear.....(Bearing in mind I am not that bothered about smoothness)
>> Edited by love machine on Saturday 22 January 14:12
Flywheel material EN24. Must be balanced. Ring gear teeth can be cut and hardened directly into flywheel circumference.
The flywheel also has to dissipate a lot of the the heat generated by the clutch so aluminium ones with a steel clutch friction ring can sometimes cause problems with cluch overheating because of poor heat transfere to the bulk of the aluminium.
Idle and low speed inertia shouldn't be a problem with a V8.
Drag from the supercharger will be a lot especially at high revs but you can avoid this on the overrun with a reciculating bypass valve (essential on roots/screw blowers, highly recomended on centrifugal types.)
The flywheel also has to dissipate a lot of the the heat generated by the clutch so aluminium ones with a steel clutch friction ring can sometimes cause problems with cluch overheating because of poor heat transfere to the bulk of the aluminium.
Idle and low speed inertia shouldn't be a problem with a V8.
Drag from the supercharger will be a lot especially at high revs but you can avoid this on the overrun with a reciculating bypass valve (essential on roots/screw blowers, highly recomended on centrifugal types.)
kenmorton said:
Flywheel material EN24. Must be balanced. Ring gear teeth can be cut and hardened directly into flywheel circumference.
The flywheel also has to dissipate a lot of the the heat generated by the clutch so aluminium ones with a steel clutch friction ring can sometimes cause problems with cluch overheating because of poor heat transfere to the bulk of the aluminium.
Idle and low speed inertia shouldn't be a problem with a V8.
Drag from the supercharger will be a lot especially at high revs but you can avoid this on the overrun with a reciculating bypass valve (essential on roots/screw blowers, highly recomended on centrifugal types.)
Thanks, that's some good info. Steel EN24 it is then!
However what's your opinion on lightening the flywheel as much as possible and allowing the pull on the crank from the SC to take up that lost inertia therefore still preventing the chance of rear wheel lock up on high rpm lift off???
I forgot to add the CR is possibly to be dropped form 10:1 to 8.5/9:1.
M
love machine said:
With my SC engine (rootes), I am running a lightened to the maximum flywheel. The supercharger will be enough of a drag anyway. I want my responsiveness. With a centrifugal blower, surely this is the worst of both worlds, belt driven and exponential boost characteristic?
Why????
All SC's are driven from the crank via belt of pulley regardless of Rootes, Whipple or Centifugal(belt driven turbo).
Agreed the torque comes in exponentially on a Centifugal, however with a V8 in a 1000kg car for mostly track day use I don't need a wall of torque from tickover, but plenty of horse power and torque higher in the rev range.
The main advantage is that a Centifugal is easier to run much more intercooled boost over a Rootes, therefore I will get more bang for my buck on the engine CR and set up.
This is because a Centifugal has a better Volumetric Efficiency creating a higher Density Ratio for the same amount of Boost pressure. High boost doesn't mean anything if it's not dense.
Roots (Eaton) are not as efficient but do produce more low down torque which is why they are fitted to many Ford/Jaguar models. But all of these are 2 tonne saloons and their engine requirements are different to mine.
A Centrifugal might be a bit more expensive (as old Eatons are so cheap on Ebay....errr.... being replaced????) but it's easier to install and intercool.
See
www.lextreme.com/icvsnic.htm
Cheers
M
joospeed said:
I follow that, but if it *doesn't* stall, why is it rougher?
Simply because a lightened flywheel gives much higher variations in crank speed.
I'm wondering if the problem is that the miniscule amount of charge in the cylinders at idel, coupled with the very low dynamic compression ratio means the charge burns very slowly, limiting how fast the piston gets pushed down even with no load at all. This means the theory about the average energy in a light and heavy flywheel being the same wouldn't hold true as a light flywheel would have to reach a higher speed during the power stroke to balance out the lower speed during compression, but the limited piston speed prevents that.
You might want to contact these experts.
www.farndon.com/flywheels.htm
I would say that EN24 is probably overkill given that ring gears are harder than the flywheel and we used to use EN19T with a calcium treatment on Jags.
I would think that EN8 was more appropriate.
You could also try aluminium with a steel friction surface.
www.farndon.com/flywheels.htm
I would say that EN24 is probably overkill given that ring gears are harder than the flywheel and we used to use EN19T with a calcium treatment on Jags.
I would think that EN8 was more appropriate.
You could also try aluminium with a steel friction surface.
Lysholm Compressor- THAT's the way to go in Super charging!
Very efficient, it has "male" and "female" compressor blades. Runs very efficiently over a wide speed-load range- often find the intercooler tank temps may be lower then a roots blower. Lysholm is still efficient in pressure ratios in excess of 2.1 :1 ( ratio of post SC to pre).
Down side is that the lysholm does internal compressive work- where as a Roots Blower supplies a volume this means at part load operation even if you by pass the Supercharger you're doing work- which will be to the detriment to fuel economy-unlike a Roots.
BTW Lysholm is alot quieter too, but that may or may not be a good thing depending on your perspective!
Very efficient, it has "male" and "female" compressor blades. Runs very efficiently over a wide speed-load range- often find the intercooler tank temps may be lower then a roots blower. Lysholm is still efficient in pressure ratios in excess of 2.1 :1 ( ratio of post SC to pre).
Down side is that the lysholm does internal compressive work- where as a Roots Blower supplies a volume this means at part load operation even if you by pass the Supercharger you're doing work- which will be to the detriment to fuel economy-unlike a Roots.
BTW Lysholm is alot quieter too, but that may or may not be a good thing depending on your perspective!
Yep. They rock 
and the part-load disadvantage is less applicable to a diesel as there's no throttle. TVR managed to get a good sound level out of one on the supercharged wedge, or so I'm told... The only real problem is the cost, which hopefully will come down as more people find out about them.
and the part-load disadvantage is less applicable to a diesel as there's no throttle. TVR managed to get a good sound level out of one on the supercharged wedge, or so I'm told... The only real problem is the cost, which hopefully will come down as more people find out about them. Skid,
Hows the conversion going? Have you been tempted to put the new motor in the Cobra ?
Just sourcing my V8 donors atm. Importing whole cars direct from Japan looks favourite and most cost effective and I think I'll be throwing a couple of CT26 Turbos in the boot for some post SVA fun......
Cheers,
Tony
Hows the conversion going? Have you been tempted to put the new motor in the Cobra ?
Just sourcing my V8 donors atm. Importing whole cars direct from Japan looks favourite and most cost effective and I think I'll be throwing a couple of CT26 Turbos in the boot for some post SVA fun......
Cheers,
Tony
Its quite simple really.
The flywheel is the root of a clutch system... It is an energy storage device and also determines the amount of power available to launch your baby.
A heavy flywheel will store more energy as it spins compared to a lighter flywheel.
If your gearing requires more power to launch, then a heavier flywheel is essential... But keep in mind that you will be slower through the gears.
In order to use a lighter flywheel, you must take into consideration the weight of the car, the RPM range she will operate at, and the crucial part - the gearing!
Steel flywheels are best suited to heavy drag cars and street performance cars.
The best choice for competition/racing cars, is a billet aluminum flywheel which is CNC machined from high-grade materials... A 1/4 inch steel friction insert is highly recommended. A highly tuned competition clutch system has a pre-determined amount of slippage at launch and on the gear changes. The flywheel insert must have enough 'mass' to absorb the heat generated by the slippage without distorting, this will make sure that your clutch life is stretched to its maximum and will provide you with consistent performance no the track.
Thinner inserts usually warp and lift leading to uneven engagement across the clutch disc. The thicker insert remains flatter and dissipates the heat better. Flywheel must be precision ground after the steel insert is installed to make sure the friction surface is parallel with the crankshaft flange for minimum runout and to provide the optimum mating surface for the clutch disc.
So, taking my advice above into consideration... and your attempt at running your beast to 8000rpm in supercharged form. I would say its best to go with a light billet aluminium flywheel with a thick steel insert. As far as your blower is concerned, I would suggest that you use a slimer belt, it all depends how much power you are aiming to push through really.
A bypass valve is CRUCIAL... so dont forget that one... and definitely dont have a cut out, its better to have a warning light and sound...
if you are worried about parasitic drag from the blower, then you can have installed a clutch between the crank and the blower, actuated via a signal from the ECU. It works well... but the sudden engagement could be an issue at higher RPM, leading to major belt slippage or worse... so you can throw that idea back in the Mad Max hall of fame.
Summary:
* An CNC'd Billet Aluminium flywheel with a thick steel insert. Properly ground to perfect parallel tolerance.
* A slimmer belt to reduce drag by allowing some slippage. Or maybe even an ECU actuated belt tensioner to control slippage when required...
* Do not go steel unless she's just a street car and/or drag car... there are many benefits to be had from an aluminium billet flywheel!
Goodluck!
The flywheel is the root of a clutch system... It is an energy storage device and also determines the amount of power available to launch your baby.
A heavy flywheel will store more energy as it spins compared to a lighter flywheel.
If your gearing requires more power to launch, then a heavier flywheel is essential... But keep in mind that you will be slower through the gears.
In order to use a lighter flywheel, you must take into consideration the weight of the car, the RPM range she will operate at, and the crucial part - the gearing!
Steel flywheels are best suited to heavy drag cars and street performance cars.
The best choice for competition/racing cars, is a billet aluminum flywheel which is CNC machined from high-grade materials... A 1/4 inch steel friction insert is highly recommended. A highly tuned competition clutch system has a pre-determined amount of slippage at launch and on the gear changes. The flywheel insert must have enough 'mass' to absorb the heat generated by the slippage without distorting, this will make sure that your clutch life is stretched to its maximum and will provide you with consistent performance no the track.
Thinner inserts usually warp and lift leading to uneven engagement across the clutch disc. The thicker insert remains flatter and dissipates the heat better. Flywheel must be precision ground after the steel insert is installed to make sure the friction surface is parallel with the crankshaft flange for minimum runout and to provide the optimum mating surface for the clutch disc.
So, taking my advice above into consideration... and your attempt at running your beast to 8000rpm in supercharged form. I would say its best to go with a light billet aluminium flywheel with a thick steel insert. As far as your blower is concerned, I would suggest that you use a slimer belt, it all depends how much power you are aiming to push through really.
A bypass valve is CRUCIAL... so dont forget that one... and definitely dont have a cut out, its better to have a warning light and sound...
if you are worried about parasitic drag from the blower, then you can have installed a clutch between the crank and the blower, actuated via a signal from the ECU. It works well... but the sudden engagement could be an issue at higher RPM, leading to major belt slippage or worse... so you can throw that idea back in the Mad Max hall of fame.
Summary:
* An CNC'd Billet Aluminium flywheel with a thick steel insert. Properly ground to perfect parallel tolerance.
* A slimmer belt to reduce drag by allowing some slippage. Or maybe even an ECU actuated belt tensioner to control slippage when required...
* Do not go steel unless she's just a street car and/or drag car... there are many benefits to be had from an aluminium billet flywheel!
Goodluck!
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