Bespoke flywheels and flywheel weight

[fasimew]

I'm looking to have a bespoke flywheel made for a project. The factory unit is a dual mass item weighing 13kg, and i'd like to opt for a single piece unit with less weight; around 30-50% less.

I've spoken about weigth with a representative of company that will be manufacturing the flywheel. He says that it's not so much about the overall weight of the flywheel, more about where you remove mass from. I agree with that, but that throws a spanner in the works as I have no idea how to go about specifying the final weight or dimensions in the terms he is expressing it. I can say remove 1kg from the inside and 5kg from the outside, but I don't think it works like that. Or does it? What do?

[dhutch]

Talk to them?

Are you trying to loose weight from the overall package, or increase speed of throttle response, or both?

[Megaflow]

You need to know a lot more than a number plucked from the air about how much you want to reduce the weight by. Do you want the inertia the same but reduced weight? Do you want lower inertia as well? Have you looked in the torsional vibration impact by removing the dual mass function?

[fasimew]

I have spoken to them. But all I get is riddles.

I'm aiming for throttle response. The only reason to make a lighter flywheel is to reduce inertia. Why else would you do it?

Torsional vibration impact is of little concern on this.

[tapkaJohnD]

You might do better by saying what the engine is, ad by asking from those who have fettled them.
The above answers are quite correct, but from a wholly general and academic background.

I've built many Triumph six-cylinder engines, both 2 and 2.5L. Triumph produced flywheels with a variety of masses, from 32lbs on the original TR6 to less than half for the Vitesse, while alloy 'wheels are available today that weigh only 6lbs. The difference is, as you say, a quicker response, but with the down side of quirky take off.
John

[ColourRestorer]

You need to do a bit of reading about moments of inertia, but in summary, when considering a rotating object, what I’ll call its rotational inertia (apologies to the pedants) is a function of the masses and the square of their distance from the axis of rotation.

So you’ll need to look at the existing flywheel, and think about it in cross section, as being the sum of its parts going from centre outwards i.e. a centre boss, then a thinner possibly tapered section, then a thicker section, and finally the ring-gear.

Each has a mass at a distance from the axis of the crank, and remember it’s the square of that distance which is important.

By considering those masses and distances you’ll start to understand what contributes the most to the rotational inertia of the existing flywheel…

...then you can start thinking about where to make changes…


In the example below I’ve shown the simplistic flywheel as five components.

The moment of inertia will be given by the sum of
( m1 x r1^2 ) + ( m2 x r2^2 ) + ( m3 x r3^2 ) + ( m4 x r4^2 ) + ( m5 x r5^2 )

Hopefully you can understand the relative significance of each part, and see why simply changing the overall mass proves absolutely nothing.

Edited by ColourRestorer on Monday 29th January 12:12

[fasimew]

It matters little what the engine is as it there may be a handful of people in the world that have put a lwfw on one. It's a V8 and they come with automatic boxes. Converting one to manual isn't common.
The dual mass flywheel is from another engine with the same crank bolt pattern. Hence, there is no point in discussing technical details to the nth degree.

I know that driveability will be affected.
The company that I'm dealing with also produces flywheels for Aston Martin's. If one of those can have a 6kg flywheel, I'm sure I'll be fine with that on mine.
What's puzzling is why they list the weight of the flywheels they produce, yet when ordering something bespoke, they make it complicated by telling me it's not as easy as saying 'I want a flywheel of x weight - where do you want the weight removed from?'.

Am I asking the right questions? Do I just tell them to remove a load of material and see where it ends up weight-wise?

[fasimew]

ColourRestorer said:

You need to do a bit of reading about moments of inertia, but in summary, when considering a rotating object, what I’ll call its rotational inertia (apologies to the pedants) is a function of the masses and the square of their distance from the axis of rotation.

So you’ll need to look at the existing flywheel, and think about it in cross section, as being the sum of its parts going from centre outwards i.e. a centre boss, then a thinner possibly tapered section, then a thicker section, and finally the ring-gear.

Each has a mass at a distance from the axis of the crank, and remember it’s the square of that distance which is important.

By considering those masses and distances you’ll start to understand what contributes the most to the rotational inertia of the existing flywheel…

...then you can start thinking about where to make changes…

I'm familiar with mechanical principles. Yes the majority of the material being removed would come from the outer portion. But why do they need to be told that? I'm asking them to make me a flywheel of x weight. Surely it's their job to fill in the blanks? I haven't gone to them with a rigid design. I've given them parameters to work to and asked them to design around that.

Do I simply need to tell them to remove as much weight from as far out as possible? I thought that would have been obvious.

Edited by fasimew on Monday 29th January 12:16

[ColourRestorer]

fasimew said:

What's puzzling is why they list the weight of the flywheels they produce...

Because if they quoted the flywheel characteristic in "kilogram metres squared" then most people wouldn't have a clue what it meant!

fasimew said:

...they make it complicated by telling me it's not as easy as saying 'I want a flywheel of x weight - where do you want the weight removed from?'.

Because they understand moments of inertia.

fasimew said:

Am I asking the right questions?

Yes, you are, but you're not analysing the answers.

fasimew said:

Do I just tell them to remove a load of material and see where it ends up weight-wise?

Only if you're prepared for a lot of trial and error before you get it right...
...and the error might include a flywheel which grenades!

[fasimew]

So as a company that designs and manufactures flywheels, why are they expecting me to provide them with a design - isn't that what I'm asking them to do? What am I missing here?

[fasimew]

Ok good point. I'll give that a go.

[HJG]

What's the application?

Don't take flywheels lightly (pardon the pun). You don't want what essentially becomes a huge and likely fragmented cutting disc coming loose or bursting at 8000rpm

[stevieturbo]

fasimew said:

It matters little what the engine is as it there may be a handful of people in the world that have put a lwfw on one. It's a V8 and they come with automatic boxes. Converting one to manual isn't common.
The dual mass flywheel is from another engine with the same crank bolt pattern. Hence, there is no point in discussing technical details to the nth degree.

I know that driveability will be affected.
The company that I'm dealing with also produces flywheels for Aston Martin's. If one of those can have a 6kg flywheel, I'm sure I'll be fine with that on mine.
What's puzzling is why they list the weight of the flywheels they produce, yet when ordering something bespoke, they make it complicated by telling me it's not as easy as saying 'I want a flywheel of x weight - where do you want the weight removed from?'.

Am I asking the right questions? Do I just tell them to remove a load of material and see where it ends up weight-wise?

It matters much. Some people have this bizarre obsession with such things, and for no valid reason at all.

If it was some ultralight pure race car, with an ultra light small diameter clutch, then ok, take things to an extreme.

So yes, the engine matters, the car matters, the application matters. The fact it had a Dual mass in the first place, likely it isn't an out and out race car to begin with, nor do you discuss the reality that the gearbox might throw a wobbler from losing the dual mass.

So perhaps better you yourself do spec everything, that way no blame can be apportioned to the maker further down the line

So is there a valid reason for needing a very light flywheel ?

[Novexx]

If they are established & already making flywheels, either they or someone else has done R&D to get these flywheels to spec. For a one off oddity you can't expect them to do R&D or some sort of trial & error set-up (the R&D may cost multiple times that of the part itself), so they are putting the onus on you.

[fasimew]

HJG said:

What's the application?

Don't take flywheels lightly (pardon the pun). You don't want what essentially becomes a huge and likely fragmented cutting disc coming loose or bursting at 8000rpm

Fast road / track car.

[fasimew]

stevieturbo said:

fasimew said:

It matters little what the engine is as it there may be a handful of people in the world that have put a lwfw on one. It's a V8 and they come with automatic boxes. Converting one to manual isn't common.
The dual mass flywheel is from another engine with the same crank bolt pattern. Hence, there is no point in discussing technical details to the nth degree.

I know that driveability will be affected.
The company that I'm dealing with also produces flywheels for Aston Martin's. If one of those can have a 6kg flywheel, I'm sure I'll be fine with that on mine.
What's puzzling is why they list the weight of the flywheels they produce, yet when ordering something bespoke, they make it complicated by telling me it's not as easy as saying 'I want a flywheel of x weight - where do you want the weight removed from?'.

Am I asking the right questions? Do I just tell them to remove a load of material and see where it ends up weight-wise?

It matters much. Some people have this bizarre obsession with such things, and for no valid reason at all.

If it was some ultralight pure race car, with an ultra light small diameter clutch, then ok, take things to an extreme.

So yes, the engine matters, the car matters, the application matters. The fact it had a Dual mass in the first place, likely it isn't an out and out race car to begin with, nor do you discuss the reality that the gearbox might throw a wobbler from losing the dual mass.

So perhaps better you yourself do spec everything, that way no blame can be apportioned to the maker further down the line

So is there a valid reason for needing a very light flywheel ?

As above, fast road / track. 1200kg. 4dr saloon. RWD. V8. NA. ITBs. Cams. Circa 500hp is the aim.

The engine was never fitted from factory with a manual gearbox. Another vehicle with a different engine (however same bellhousing and crank bolt pattern) was fitted with a manual box. Find me an average road car within the past 20 years that didn't come with a dual mass.
Losing the dmf shouldn't affect the gearbox in such a way. I've never heard of it at least. The friction disc will be sprung anyway.

Is 6-8kg very light? I've seen much smaller displacement engines with flywheels that weigh even less. It shouldn't be an issue on a V8.

[fasimew]

Novexx said:

If they are established & already making flywheels, either they or someone else has done R&D to get these flywheels to spec. For a one off oddity you can't expect them to do R&D or some sort of trial & error set-up (the R&D may cost multiple times that of the part itself), so they are putting the onus on you.

Fair point. I'll chase it up.

[stevieturbo]

fasimew said:

As above, fast road / track. 1200kg. 4dr saloon. RWD. V8. NA. ITBs. Cams. Circa 500hp is the aim.

The engine was never fitted from factory with a manual gearbox. Another vehicle with a different engine (however same bellhousing and crank bolt pattern) was fitted with a manual box. Find me an average road car within the past 20 years that didn't come with a dual mass.
Losing the dmf shouldn't affect the gearbox in such a way. I've never heard of it at least. The friction disc will be sprung anyway.

Is 6-8kg very light? I've seen much smaller displacement engines with flywheels that weigh even less. It shouldn't be an issue on a V8.

And does the engine have any other form of harmonic, or other damping ? internally or externally balanced ? Is the flywheel a critical part of this engine ?

A V8 would tend to have a larger diameter flywheel, hence larger heavier flywheel....so depends on what of that is being retained, and clutch.

And of course some gearboxes will fail when people remove a DMF and fit a solid setup, it's very common. Which is why not all setups are available with a swap kit as they are known to cause trouble in the past.

[Megaflow]

fasimew said:

As above, fast road / track. 1200kg. 4dr saloon. RWD. V8. NA. ITBs. Cams. Circa 500hp is the aim.

The engine was never fitted from factory with a manual gearbox. Another vehicle with a different engine (however same bellhousing and crank bolt pattern) was fitted with a manual box. Find me an average road car within the past 20 years that didn't come with a dual mass.
Losing the dmf shouldn't affect the gearbox in such a way. I've never heard of it at least. The friction disc will be sprung anyway.

Is 6-8kg very light? I've seen much smaller displacement engines with flywheels that weigh even less. It shouldn't be an issue on a V8.

2008 Fiesta ST150 doesn’t have a dual mass flywheel. There is a thread on here somewhere about lightweight flywheels where a chap called Max Torque, who has sadly left, explains why the TV from an engine with its DMF removed can very much effect a gearbox.

In years gone by, before the days of very accurate FEA, there was some much spare capacity in your average crankshaft and block that removing the DMF would have no impact, no so much the case these days.

[Novexx]

If I were in this predicament I think I would be looking for a (any) vehicle with a similar engine specification & transmission layout that a lightened flywheel is available for. If you can get it, the spec difference between standard & lightened flywheel could be used as a starting point / guideline for how much & where.