Light weight flywheel thoughts

[little fella]

Hi guys,

Was just wondering about maybe changing to a light weight flywheel and clutch.
I've seen a kit from rpm technik thats reasonably priced.
Does the lighter flywheel make much difference to performance or does it make the car harder to drive?
I've also recently heard that they can snap the crank, is that true?

Carl

 

[Paynewright]

Most modern manual cars have a dual mass flywheel which is effectively two bits of iron stuck together with some special rubber type mastic. The purpose of this is to absorb any unwanted vibrations along the crankshaft (and prevent it cracking) . Older vehicles tent to have a similar two part pulley on the front of the engine to drive the water pump / alternator.


Fitting a lightweight flywheel is usually in the realms of motorsport, where everything is fettled / optimised for performance. Usually the crankshaft / flywheel / clutch / front pulley assembly are balanced together to much finer tolerances than the production line meaning the unwanted crank vibrations are greatly reduced. That said you could plonk a LWFW on your engine and it be completely fine.

I have a light flywheel on my caterham (3.2kg as opposed to 7kg+) and it accelerates faster, slows quicker with engine braking and changes gear better. However, it is hard work in traffic needing more revs to stop it stalling. Its all to do with the rotating mass the engine has to move. Lighter flywheels are usually steel which is much stronger than cast iron and less prone to exploding when weight is removed!

I hope that helps.

 

[Shalmaneser]

Most modern manual cars have a dual mass flywheel which is effectively two bits of iron stuck together with some special rubber type mastic. The purpose of this is to absorb any unwanted vibrations along the crankshaft (and prevent it cracking) . Older vehicles tent to have a similar two part pulley on the front of the engine to drive the water pump / alternator.


Fitting a lightweight flywheel is usually in the realms of motorsport, where everything is fettled / optimised for performance. Usually the crankshaft / flywheel / clutch / front pulley assembly are balanced together to much finer tolerances than the production line meaning the unwanted crank vibrations are greatly reduced. That said you could plonk a LWFW on your engine and it be completely fine.

I have a light flywheel on my caterham (3.2kg as opposed to 7kg+) and it accelerates faster, slows quicker with engine braking and changes gear better. However, it is hard work in traffic needing more revs to stop it stalling. Its all to do with the rotating mass the engine has to move. Lighter flywheels are usually steel which is much stronger than cast iron and less prone to exploding when weight is removed!

I hope that helps.

I think you're getting the a dual mass flywheel confused with a vibration damper which works as you describe. DMF's are quite a bit more complex:

https://www.youtube.com/watch?v=YnaXB8q3uzQ

But the thrust of your argument is fair, the chances of increased vibrations ruining the motor are higher. If the OP is willing to roll the dice then it might be a nice mod! I know some here have them fitted and are very happy with them.

 

[Paynewright]

Just shows how much I really know

I knew they were for damping vibrations and thought it was to protect the engine rather than to isolate engine vibrations from the drive train.

The pulley damper bit and effects of the LWFW are (mostly) correct!

 

[infrasilver]

Ideally you would want to balance the crankshaft and LWFW together to eliminate vibration, the overhang of the M96 crankshaft can cause it to break if not balanced and there is any vibration caused?
This is my usual reply to this question as I know it does happen and it is better to be warned about the potential issue, others will give you a more positive response.

 

[Jamesx19]

I gave a lot of thought to fitting one when I had my engine rebuilt.

There are a few threads on the forum that tackle the pros and cons, but I think the first posts on this topic summarise the argument nicely.

My own observation, is that no one posted that it was a brilliant modification that they would do again. Every Porsche garage or mechanic I spoke to said they wouldn't recommend fitting one.

I decided not to go that route. But if I was building a more track focused or occasional use fast road blaster, then I think all the issues that get mentioned could be either tackled or lived with.....

Pay your money etc??

 

[little fella]

Thanks for the replies guys some good info there, I never thought about extra
vibration through the crank.
Though I did wonder if it would make it easier to stall in traffic.
I don't wanna risk breaking anything in the engine as the previous owner spent
10k on it at hartech, so will stick with my standard flywheel and clutch.

Carl :thumb:

 

[1marc]

I'd give Hartech a call and see if they recommend it. RPM fit them. I've had them in a few others cars and love them due to the freer revs. The chatter has always been minimum, and something that occurs in very low revs and a higher gear when you build the revs slowly. It's a bit like having an aftermarket exhaust that has a bit of drone at a specific rev range, you just get used to it and drive around it.

 

[little fella]

I'd give Hartech a call and see if they recommend it. RPM fit them. I've had them in a few others cars and love them due to the freer revs. The chatter has always been minimum, and something that occurs in very low revs and a higher gear when you build the revs slowly. It's a bit like having an aftermarket exhaust that has a bit of drone at a specific rev range, you just get used to it and drive around it.

It's the fact that it's been pointed out to me there is i slight risk of breaking the crankshaft when using a light weight flywheel that's put me off.

 

[1marc]

I'd give Hartech a call and see if they recommend it. RPM fit them. I've had them in a few others cars and love them due to the freer revs. The chatter has always been minimum, and something that occurs in very low revs and a higher gear when you build the revs slowly. It's a bit like having an aftermarket exhaust that has a bit of drone at a specific rev range, you just get used to it and drive around it.

It's the fact that it's been pointed out to me there is i slight risk of breaking the crankshaft when using a light weight flywheel that's put me off.

Yeah I find that concerning too, but I'd want to investigate it fully with someone like Hartech personally, before ruling out. 👍

 

[Marky911]

I personally wouldn't on an m96 engine.
I had my box rebuilt when I had my C2 and toyed with the idea after having one on my old GT3.
They do feel better and the free revving is nice but I just thought it wasn't worth the possible hassle.

Even if I was fitting a new clutch to my current GT3, I'm not sure if I'd add the LWFW. 50:50 mind, I'd have a good think.

As I say though, not on an M96 motor. The less reasons you can give one of them to fail the better and I'm not being funny there, it's just sensible. :thumb:

 

[deMort]

Every Porsche garage or mechanic I spoke to said they wouldn't recommend fitting one.

Yup

i'm no expert in after market mods at all which most of you know .. but i have seen a snapped crankshaft that had a light non DMF flywheel fitted ..

As i understand it the take up shock load to the crankshaft can cause this to happen .

Balancing the crank makes this better ??? 9E would be the people to talk to about the pros and cons of this i feel .. it's who i would talk to anyways .

 

[infrasilver]

I've still got a paperweight from when my DMF got a little unbalanced on a track day and my reason for always sounding like a broken record when someone asks about fitting a LWFW

 

[MaxA]

I've had a LWFW in a couple of cars (and I still own and track one of them, not my 997), but not everyone can be bothered with the additional noise (chatter), the likelihood to stall or the risk of crankshaft failure. And they're useless for engine braking too, as the engine just spins up when you come off the clutch on a downchange. :dont know:

On the other hand, they feel great, so much more zingy and responsive. :thumb:

 

[little fella]

100% not getting a light weight flywheel now, just thought it might be a good mod for when i get 2nd gear refreshed at some point as it does crunch when cold if I'm not careful.

Carl :thumb: