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Stock flywheel weighs 12.8 kilos.
Joshies light weigh flywheel weighs 6.4 kilos.
You will not be able to lighten the stock flywheel, assuming thats the one you have lined up to lighten, down to 6.4 kilos without destroying it.

The stock flywheel is a dual mass set up with pockets and springs hidden under the surface. You could not cut it away to lighten it by any significant amount to make it worthwhile and still retain its integrity. Just disguard it for a single mass light weight flywheel, assuming its you intention to get the engine to spool up quicker.

not that i'm cynical or anything karl, but you have just released a flywheel for the s4/rs4 haven't you?

Wish i'd known more about them b4 i bought the one i've got, what are the differences between yours and the mtm one?

not that i'm cynical or anything karl, but you have just released a flywheel for the s4/rs4 haven't you?

Wish i'd known more about them b4 i bought the one i've got, what are the differences between yours and the mtm one?

You are correct Jon.
I have not seen an MTM flywheel but I am sure that Kim at QST or Scott at AMD would have and they have both seen my flywheel as well. Maybe they would be the best people to explain the differences.
What I do know is that my flywheel accepts the standard RS4 clutch pressure plate and driven plate. I beleive the MTM one accepts a higher rated clutch set up.

yeah mate, the mtm one only fits thier clutch, so you have a distinct advantage over the competition

So what's a dual-mass flywheel then apart from misnamed (mass only starts increasing quite near the speed of light).

Presumably there are weights inside which shift outwards when it turns at high speed, giving it more inertia at high revs than low???

So therefore what is the downside of a single-mass lightweight flywheel compared to a heavier dual-mass one?

i know my car destroys the dual mass flywheels due to the amount of torque, but has more judder with the lighter one. so it's a bit of a trade off

So what's a dual-mass flywheel then apart from misnamed (mass only starts increasing quite near the speed of light).

The dual-mass flywheel is designed to absorb engine vibrations before they are transmitted to the driveline where they can create gear rattle. This is achieved by splitting the conventional flywheel into two sections: a primary section, which bolts to the crankshaft, and a secondary section, onto which the clutch is bolted.
The primary section of the flywheel contains springs to isolate engine vibrations and a torque-limiting device to prevent engine torque spikes from exceeding engine and transmission component strength. When torque spikes occur, the torque-limiting package allows the primary section of the flywheel to turn independently from the secondary section. I think that means its not misnamed [img]images/graemlins/shocked.gif[/img]

Presumably there are weights inside which shift outwards when it turns at high speed, giving it more inertia at high revs than low???

No.

So therefore what is the downside of a single-mass lightweight flywheel compared to a heavier dual-mass one?

More gearbox noice in the car and less forgiving to the driver who misses gear changes.

From my experience so far with one of Karl's flywheels.

The only real downside is a metallic 'rattle' if you accelerate hard from below 2K revs.
This dissapears as soon as you are above 1K9 ish and can be eliminated by either driving like a granny up tp 2K or dropping a gear in anticipation.

Otherwise they are marvelous, engine spins up much quicker and the turbo's therefore spool up quicker.

Thanks Karl - I stand corrected.

Presumably the downside of the single-mass is not just noise - but risk of gearbox damage?

(N.B. I'm not intentionally being critical here - I just want to understand the risks).

Another side effect of a lighter flywheel is normally a lumpier tickover (less mass to keep the engine rotating).
Sometimes it may also mean the engine will stall when dipping the clutch from higher revs. This is normaly overcome by increasing the tickover slightly.

BTW, dual-mass flywheels are standard on most of the porsche range too, except the RS. People changing to the RS flywheel generally experience the above, unless they raise the tickover.

Cheers,
John.

Presumably the downside of the single-mass is not just noise - but risk of gearbox damage?

The single mass flywheel will not damage the gearbox.

(N.B. I'm not intentionally being critical here - I just want to understand the risks).

No problem. I would ask the same questions.