Flywheel lightening

[crispy'86]

Alright after a bit of reading up on everyone's mixed opinions about machining/lightening flywheels. Some have said any machining is frowned upon, and others say a little is alright. here's my major question:

How much is too much when reducing material on the back of the flywheel?? I have 2 flywheels, both have been lightened but one more than the other,
1st is a 16v unit, machined off the back and front faces, leaving 1-2mm around the bolts and locating dowes for the pressure plate weighed it at 7.8kg
2nd is a blacktop unit with minimal material taken off back only weighin 5kg (note: the scales have an inaccuracy of around .2kg, zeroed them in everytime i weighed them, checked both several times)
Now i know the 16v unit i'm not going to touch as it leaves no strength of holding the pressure plate on, the 20v unit however, is 900 grams too much to be taken off the back to safely use it??
Bear in mind the 16v flywheel was in my race car and have done several events with it.

[edwagon]

Ive got a book here '21st century performance' which condones lightening stock flywheels, but it does say that taking too much off, especially from the wrong place, is asking for trouble.

I think that 'how much' and 'where from' is the key - for both strength AND rotational inertia!

Got any photos of the flywheels in question?

I personally wouldn't lighten a stock flywheel at all, Its asking for sht imho , but you're doing the right thing by asking and im sure that a sensible amount of machining in the right place can't hurt.

[MRDRFT]

my dad lightens flywheels at his work if you want you could go ask at his work what they say as your in chch. Engin Reconditiong Services 437 st asaph st. east side of fitz ave.im sure they can help alot.

[sergei]

There is no point in doing it on a street car.
I have swapped to a Blacktop flywheel on a Silvertop, and there was no difference what so ever.
Also my friends brother put 4.2Kg Tom's (or some other brand I can't remember) on a Silvertop and that made no difference as well.
In my opinion it is complete waste of time and money.
4AGE (20v) flywheel compare to 3SGTE for example is ultra small and ultra light anyway. Not that 3SGTE has any problems revving that.
Heavy flywheel is good - it helps with uneven load (rough road for example), smoothes out the vibrations and helps engine at low rpms. Factory flywheel will accelerate a lot faster then the car in 1st gear anyway (especially 4AGE) so there should not be any problems what so ever.

[Bling]

its for his race car (FXGT)

[crispy'86]

Yes as Luke said, it's for my race car , 4age with minor engine mods for now anyway. Reason i ask is when i had to get a clutch i got given a flywheel to use, now i don't think this one is really strong enough. And the blacktop unit i have has already been lightened on the back where it has been machined near the outer circumference of the flywheel. I will get pics up as soon as i can so you all can see the differences.

[ChaosAD]

blacktop flywheel is basically a silvertop flywheel that has been lightened at factory. It aint a standard blacktop is it?

[crispy'86]

definitely looks like a slightly lightened blacktop flywheel as the drillings to balance it have been slightly machined off on the rear of it

[crispy'86]

some pics of the comparisons. Blacktop flywheel on the right, bluetop on left of the flywheels beside each other. The first 2 pics are the bluetop flywheel, 3rd blacktop one
you can see my concern now that you've got proof of how much has been machined off the bluetop unit

[Bling]

that post confuses the s**t out of me bro, you sure the blacktop is lightened?

[AceSniper]

blacktop one looks safe, guess its had a very light skim, but were its been done it wont effect strength I doubt

[crispy'86]

blacktop one looks safe, guess its had a very light skim, but were its been done it wont effect strength I doubt

that post confuses the s**t out of me bro, you sure the blacktop is lightened?

So you see why i think the blacktop has been slightly machined/skimmed. You all can see how i feel the blacktop unit is the one i'd feel safer to use for obvious reasons.