3B flywheel

[nip]

how much is the ideal amount to lighten the flywheel by, and any pro`s and con`s
cheers

[driftin jo]

There is no ideal weight, it just depends how you want the engine to behave.
If you go very light then you will have to have your idle set at ~1500rpm.
The more weight you remove the more likely it is you will stall if you don't give it enough revs when you let the clutch out as you don't have enough inertia .
So it all depends on what you want/driving stile etc etc.
Having less weight will give you more acceleration in lower gears especially first but higher gears there will be very little difference.
I did a very light one for a friend and it revved like a Ferrari , touch the throttle and you hit 7000 revs in a split second, this also brings the danger of over revving the engine if you miss a gear or something breaks and trust me your ecu will not be able to cut the power quick enough to keep the revs down.
My friends one sat at idle would hit 8000 rpm if you put your foot to the floor even though the ecu was cutting at 7400, it would drop back to 7400 and hold that but accelerating up with no load it could not keep the limit.

The link is a good article about the subject and gives you an idea of how much equivalent weight loss there would be for each gear as I mentioned above.

http://www.pumaracing.co.uk/FLYWHEEL.htm

[nip]

There is no ideal weight, it just depends how you want the engine to behave.
If you go very light then you will have to have your idle set at ~1500rpm.
The more weight you remove the more likely it is you will stall if you don't give it enough revs when you let the clutch out as you don't have enough inertia .
So it all depends on what you want/driving stile etc etc.
Having less weight will give you more acceleration in lower gears especially first but higher gears there will be very little difference.
I did a very light one for a friend and it revved like a Ferrari , touch the throttle and you hit 7000 revs in a split second, this also brings the danger of over revving the engine if you miss a gear or something breaks and trust me your ecu will not be able to cut the power quick enough to keep the revs down.
My friends one sat at idle would hit 8000 rpm if you put your foot to the floor even though the ecu was cutting at 7400, it would drop back to 7400 and hold that but accelerating up with no load it could not keep the limit.

The link is a good article about the subject and gives you an idea of how much equivalent weight loss there would be for each gear as I mentioned above.

http://www.pumaracing.co.uk/FLYWHEEL.htm

Cheers thanks jo, So 1 kg should be enough

[chezz]

Jo,You forgot to mention the possibilty of the crank shattering and taling the entire engine out...the harmonics are being screwed up - totally.

[dspl1236]

unless you have a dynamic crank dampener

[chezz]

one that was set up in a factory that was calculated to be matched to a rotating mass at the other end called a flywheel, that on mate?

[driftin jo]

one that was set up in a factory that was calculated to be matched to a rotating mass at the other end called a flywheel, that on mate?

No it wasn't.

It was designed to damp out harmonic vibrations from the crank that are only an issue on the none drive end i.e. the pulley. The flywheel end has a very large mass i.e. the gearbox and entire drivetrain, thus this end of the crank it totally free from torsional whip due to very large inertia, there would be no problem in this respect even if your flywheel weighed 1kg as this end of the crank is the output end.

[chezz]

And when it is neutral and revving at some silly figure that it was never designed to reach it's shaking the engine to pieces.

[driftin jo]

And when it is neutral and revving at some silly figure that it was never designed to reach it's shaking the engine to pieces.

how much load do you think you can have in neutral ?
It takes no power at all to spin an engine in neutral, you hardly put any power through the crank in neutral and your at the limiter.
No stress on the crank at all.

The other point is that destructive torsional vibrations are mostly caused when an engine is under load and is at a given rpm long enough for them to build up, e.g. when driving up a hill at a constant speed, this is the scenario that the torsional vibration damper in the front pulley is there to deal with.