Benefits of a lightened flywheel ?

Sneaky Peaky · 14 May 2007 at 21:38

My oem clutch is slipping (to be expected) so is in the shop on Friday for an Exedy Stage 1 Organic. Whilst looking around though I have been getting mixed views on getting a lightened flywheel at the same time..

One tuner in particular raved about them saying there are only upsides in terms of free revving etc and no downsides in terms of driveability..

Other people have said though that it can be very tiring to drive especially in traffic with more of an on/off feeling..

What's peoples views ? I would be getting the Exedy lightened racing flywheel which is 5.75kg

Many Thanks

megakid · 14 May 2007 at 22:10

Isnt idling a problem with lightened flywheels? I heard it can cause lumpy idle

NightShadow · 14 May 2007 at 22:17

I was under the impressing that as the mass is less the accel and responsiveness improve but also because it is lighter it spins down quicker so to speak as there is less weight to keep the spinning momentum. Thats my understanding anyways

NS

Acolyte · 14 May 2007 at 22:20

megakid said:
Isnt idling a problem with lightened flywheels? I heard it can cause lumpy idle

The trick is to lighten it yet still keep it just heavy enough to keep it idleing well.

The_Dark_Side · 14 May 2007 at 22:27

megakid said:
Isnt idling a problem with lightened flywheels? I heard it can cause lumpy idle

depends which engine you're talking about and by how much the flywheel is lightened.
the primary function of a flywheel is to smooth out the rotation of the crank as it's basically just a big piece of pig iron that uses it's mass to stop the revs from hunting all over the place.
nowadays as mass production engineering standards and tolerances increase to levels only seen in the exotic and exclusive engines of 10/20 years ago, the flywheel is becoming redundant.
at some point in the not-to-distant future the typical mass produced car won't even have a flywheel as such, merely some type of surface plate to bolt the clutch onto.

Fett · 14 May 2007 at 22:30

I was tempted once but the cons that were explained to me (for normal road driving) outweighed the positive effects. Higher fuel consumption, bearing life and careful throttle modulation around town etc did not (to me) seem worth it.

Dogbreath · 14 May 2007 at 23:21

Lightening the flywheel provides the same benefits as lightening the car, only because the effect of the flywheel is multiplied by the gear ratio it's even more effective in low gears. There is no reason why this should provide worse fuel economy, unless you are driving the car quicker as a result of the better acceleration in lower gears.

Simon · 14 May 2007 at 23:26

The_Dark_Side said:
at some point in the not-to-distant future the typical mass produced car won't even have a flywheel as such, merely some type of surface plate to bolt the clutch onto.

4 cylinder engines will always need a flywheel.

Confused · 14 May 2007 at 23:30

I've put a lightened flywheel on my Prelude, as have many, many others on PreludeUK.

The OEM flywheel is 19lbs, the lightened is 8lbs. Idling (which is about all my engine has done so far with it, as it's off the road) is still perfectly fine. It does rev quicker (with no load), and the revs drop off quickly again too, but the ECU always catches it and keeps it idling properly.

The only movement of the car I've done is driving it in and out of the garage to work on various bits of it, so it's very low-rev, low-throttle movement. I can honestly say it's just as easy to move around with little or no throttle as it was with the OEM flywheel! Other PreludeUK members also report very similar findings, that the low-speed driveability isn't impaired by the fitting of the lightened flywheel.

The_Dark_Side · 14 May 2007 at 23:39

Simon said:
4 cylinder engines will always need a flywheel.

it takes a brave man to make a prediction that includes the word "always".
what makes you so sure?

Simon · 14 May 2007 at 23:48

The_Dark_Side said:
it takes a brave man to make a prediction that includes the word "always".
what makes you so sure?

A flywheel smooths pulses from each of the cylinders, without one most engines wouldnt idle. They would also feel very rough.

Modern diesels have dual mass flywheels that go one step further to smooth this problem out.

The_Dark_Side · 15 May 2007 at 00:38

Simon said:
A flywheel smooths pulses from each of the cylinders, without one most engines wouldnt idle. They would also feel very rough.

i totally agree.
my point was that as engine tech improves there will come a point when the flywheel isn't needed as a form of damper as the motor will be more finely balanced.

diesls may be a different story due to their very nature.

Simon · 15 May 2007 at 00:41

The_Dark_Side said:
i totally agree.
my point was that as engine tech improves there will come a point when the flywheel isn't needed as a form of damper as the motor will be more finely balanced.

diesls may be a different story due to their very nature.

Ermm, you dont really understand engines.

Diesels are no different they just have much stronger pulses. All engines are already pretty much perfectly balanced hence why some can rev past 8,000rpm. No matter what you will always have only 2 pulses per engine rotation

All cars will always have a flywheel anyway in the form of a clutch. The only engine that won't is an electric engine as this is virtually an infinite cylinder engine

Dogbreath · 15 May 2007 at 00:43

You simply can't perfectly balance a 4 cylinder engine without extra balancer shafts, and irrespective of the balance issue, a 4 cylinder engine simply doesn't provide consistent torque through each rotation, so a flywheel is required.

The_Dark_Side · 15 May 2007 at 00:45

Simon said:
Ermm, you dont really understand engines.

oh i've got a reasonable idea how the waffle sprocket is retained by the giggling pin, i can assure you.
what i meant was the vibrations generated by a compression ignition lump are generally of a higher magnitude than those of a modern petrol engine and as such would be much harder to dampen purely by using engineering of a higher precision.

The_Dark_Side · 15 May 2007 at 00:47

Dogbreath said:
You simply can't perfectly balance a 4 cylinder engine without extra balancer shafts, and irrespective of the balance issue, a 4 cylinder engine simply doesn't provide consistent torque through each rotation, so a flywheel is required.

indeed it is, but i did say there will come a time when the flywheel will be engineered out of the system.
can you really be 100% sure this cannot happen?

Simon · 15 May 2007 at 00:49

The_Dark_Side said:
oh i've got a reasonable idea how the waffle sprocket is retained by the giggling pin, i can assure you.
what i meant was the vibrations generated by a compression ignition lump are generally of a higher magnitude than those of a modern petrol engine and as such would be much harder to dampen purely by using engineering of a higher precision.

Its not a vibration issue though. Its purely a linear impulse acting on a rotating object, with no momentum in the system worst case scenario is that the engine would stop before the next impulse (power stroke off the following piston)

Now imagine how rough it would be if the engine was just about to stop at idle and there was a massive lump off torque thrown in to speed it up, as you can imagine it wouldn't be smooth.

Simon · 15 May 2007 at 00:50

The_Dark_Side said:
indeed it is, but i did say there will come a time when the flywheel will be engineered out of the system.
can you really be 100% sure this cannot happen?

As an Automotive Engineer who studied engine dynamics, yes I can

The_Dark_Side · 15 May 2007 at 00:53

Simon said:
Its not a vibration issue though. Its purely a linear impulse acting on a rotating object, with no momentum in the worst case scenario then the engine would stop before the next impulse (power stroke off the following piston)

Now imagine how rough it would be if the engine was just about to stop at idle and there was a massive lump off torque thrown in to speed it up, as you can imagine it wouldn't be smooth.

i wouldn't even attempt to suggest i have a grasp of engine dynamics anywhere near as well as yours. after reading a lot of your posts it's clear you're very familair with some pretty in depth concepts, some of which make a nice whooshing noise as they perform a fly-by over my head.
but i've read this "no flywheel" idea a few times from a few different sources and to the relative layman (me) it does sound possible.

Simon · 15 May 2007 at 00:55

The_Dark_Side said:
but i've read this "no flywheel" idea a few times from a few different sources and to the relative layman (me) it does sound possible.

You could remove a flywheel but then where to you mount the clutch.

In any case there will always be the crank and clutch to act as a 'flywheel' anyway. A flywheel being something that stores energy in the form of momentum