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[zirk]

IMHO, it doesn't make much sense in an Omega. I have gone from a 15kg flywheel to a 6kg flywheel in my Westfield, which weighs in at about 650kg and revs to 7400 RPM and I can't say there was a huge difference in performance. Might have made it a little quicker in 1st (which is traction-limited most of the time anyway) but in higher gears the dominant factor is the weight of the car (and an Omega has an extra tonne of that).

It does make quick gear changes a little easier due to the fact that the rev drop between gears happens quicker but the Omega's manual box is a bit agricultural anyway, IMHO.

If you are ditching the DMF make sure you also change to a sprung clutch driven plate to absorb the shocks in the transmission.

Be VERY careful if they are lightening a flywheel rather than fabricating a light one. You do not want it to be weakened and at risk of bursting.

Kevin

You mean get the Black and Decker out and whack some holes in it, Hmm, vented clutch. 

[feeutfo]

thought from posts on here, that the only differance in plod state of tune was the dif?

[aaronjb]

Be VERY careful if they are lightening a flywheel rather than fabricating a light one. You do not want it to be weakened and at risk of bursting.

Oh yeah - I would also never recommend machining a flywheel to make it lighter..

Because let's face it, you don't want to end up with a car looking like this: http://boardroom.wscc.co.uk/cgi-bin/ikonboard.cgi?act=ST;f=3;t=52365

[Kevin Wood]

You mean get the Black and Decker out and whack some holes in it, Hmm, vented clutch. 

I sincerely hope not.

Wherever you machine it you will lose strength. Drilling holes is probably a bad idea because the holes will act as stress raisers for the surrounding material.

The greatest benefit is to lose mass towards the outer edge of the flywheel as it is this mass that is accelerated to the highest speeds by the rotation of the flywheel and hence its' effect is multiplied by its' angular velocity.

Strength is most critical towards the centre of the flywheel which is subject to forces trying to pull the flywheel apart and also to the torque output from the crankshaft. This itself comes in pulses as each cylinder fires so there is a lot of vibration coupled into the flywheel at this point.

If you're going to machine a flywheel it is therefore better to concentrate on the outside and ensure enough strength is left towards the centre.

Go to someone who doesn't appreciate the job the flywheel is doing and it could cost you your ankles. There is a lot of energy stored in a flywheel and if it lets go at high RPM it will destroy everything in its' path, including the bellhousing, transmission tunnel and the parts of the biological seat-to-steering wheel interface that sit just the other side of the transmission tunnel.

http://www.youtube.com/watch?v=jBONiZ6Hv1c

The other thing which hasn't yet been touched on is that the flywheel acts as a heatsink for the clutch. Not really a problem in racing and fast road applications because the clutch is rarely required to dissipate a lot of heat except when accelerating from a standing start but try to tow a caravan through the Pennines and you might find a failure mode here.

Kevin

[kcl]

thought from posts on here, that the only differance in plod state of tune was the dif?

You are right, there is still no such thing than "police special -tuned" Omega. All engines, no matter what application was, are the same. Also, no different maps/ECU's were ever available from factory, nor dealers.

Urban legends live strong.

[serek]

thought from posts on here, that the only differance in plod state of tune was the dif?

had plod LSD on mine omega 3.0 and cant really see any different to standars diff
I got now 4.22 diff  on 3.2 manual and this make huge different , but use some more fuel and top speed is 140MPH

[feeutfo]

drove a 3.2 plod last month, bloody shifts compared to mine on petrol, revs 500 odd rpm higher at 70mph so it will drink fuel, which was one of the owners complaints.

offered to swap for my dif, he rightly refused saying he would look into lpg conversions, which sounds right to me.

[Omega6pot]

some police cars definately had chipped ecu's, i dont think vauxhall special vehicle services had anything to do with it, instead i think some police workshops did this to increase power for there drivers. Not wildy done perhaps but the ex-police car i had revved past 7 and really shifted, drank fuel something shockin aswell haha

[2woody]

right then .....

Lightened flywheels.

the flywheel is there to store energy in the engine. This is used to smooth out the vibration caused by the pistons having to stop and turn round twice per revolution.

Heavy flywheel = better smoothing = low vibration
Light flywheel = worse smoothing = high vibration

applies when under load or at idle.

HOWEVER. Lightening the flywheel does have a very significant effect on the gearing. Because the rotational inertia is connected to the ground through the gearbox, then any reduction in rotational inertia has a greater effect in the lower gears. I'd make a reasonably-informed guess that taking 10kg out of the flywheel would cause the car to accelerate as if its 200kg lighter in 1st gear and then accelerate as if it were 125kg lighter in 2nd, right up to "no effect" in 4th.


DMF.....

the dual mass flywheel is something entirely different. Put simply, the DMF puts the majority of the vibration-smoothing weight on the gearbox-side of the clutch, where it can reduce drivetrain noise and vibration.

Changing to a single-mass unit could induce a bit of drivetrain noise, but you'd be hard-pressed to notice. Usual noise is a sort of "zizzle" coming from the gearlever at very low revs/high load.

hope this is of help - if I put all of the theory in this, we'd be here all week

[aaronjb]

hope this is of help - if I put all of the theory in this, we'd be here all week

The links I posted had the theory (At least for calculating lost 'mass' from lost rotational mass) And you're right.. it's long.. and boring..

Unless you like algebra of course

[2woody]

I have to do that sort of thing for a living....!

[aaronjb]

I have to do that sort of thing for a living....!

My condolences.. 

(I jest, I love the engineering, maths & physics that lies behind cars, as well as taking them apart & putting them back together better.. though I'm still not sure I'd want to do it as a job )

[tunnie]

some police cars definately had chipped ecu's, i dont think vauxhall special vehicle services had anything to do with it, instead i think some police workshops did this to increase power for there drivers. Not wildy done perhaps but the ex-police car i had revved past 7 and really shifted, drank fuel something shockin aswell haha

Nah, they all run standard setup as retail cars

[kcl]

some police cars definately had chipped ecu's, i dont think vauxhall special vehicle services had anything to do with it, instead i think some police workshops did this to increase power for there drivers. Not wildy done perhaps but the ex-police car i had revved past 7 and really shifted, drank fuel something shockin aswell haha

Nah, they all run standard setup as retail cars

This really is a tough one for some of us... Please, show me two things:
1. a chipped ECU for a petrol Omega with dyno-graphs before and after chipping
2. any evidence, other that hear-say, of any tuning of any Omegas made by GM or local representative (or the local police or whatever...)
After these I just might be able to accept the slight possibility that there may have been someone somewhere who has been able to really tune-up a petrol V6 Omega.

For the OP: you say you have "felt the Vectra being quicker" etc... any documents of the facts it really gained something by lightening the flywheel?

[Kevin Wood]

This really is a tough one for some of us... Please, show me two things:
1. a chipped ECU for a petrol Omega with dyno-graphs before and after chipping
2. any evidence, other that hear-say, of any tuning of any Omegas made by GM or local representative (or the local police or whatever...)

Well, we know that aftermarket chips are available for earlier Omegas and I guess it's not impossible that the fitting of them might have been included in the Police spec. I have to say I'm with Tunnie, though. There's no evidence to suggest that any tuning was carried out on Police spec. cars.

As to dyno graphs, they are so easily "tweaked" to show what the punter wants to see as to be almost worthless, IMHO, unless you know the rolling road operator and are sure he operates a "no bull" policy, keeps the rolling road calibrated and does a proper coastdown to compensate out the losses.

For the OP: you say you have "felt the Vectra being quicker" etc... any documents of the facts it really gained something by lightening the flywheel?

You're really getting into difficult territory here because we're talking about dynamic power delivery where d_RPM/d_t is very important. Even a dyno won't show that because cars are generally tested on a dyno in a high gear with a fairly low d_RPM/d_t, so the effects of a lightened flywheel will not be noticeable.

A lightened flywheel absolutely won't affect the steady state power output of the engine, only when it is accelerating quickly (since less energy is absorbed accelerating the flywheel). I have great difficulty believing that it affected the fuel consumption.

Mods such as this are pure physics. You can calculate what they will change despite what the seat of your pants might be telling you. The seat of the pants will tell you that the car gets faster after you've washed it, after all.

Kevin