as winfred said basically....
The stock unit's 33lbs (on a 5 speed) and stores a boatload of energy. Helps low end torque and smoooooth shifting. A lighter unit will allow the engine to rev marginally faster both engaged and in neutral.
I have the 22 lbs E28 setup and Martin has 15 lb lightened E28 setup. The engines have better throttle "blip" response for downshift rev matching. I don't think they are really any faster accel wise.
I think the best reason to put in an E28 setup is cause the flywheels are mucho cheaper than a replacement dual mass. They can be resurfaced as well. If you are a real performance geek and want to have faster rev matching during downshifts, might put one in. Other than that, not much to talk about.
Jeff
90 535i, E28 flywheel and clutch setup

Originally Posted by
jplacson
What's the disadvantage of those newer AL flywheels over the stock dual-mass ones? I know the stock isn't the best one around, but I'm sure BMW placed it there for a reason... what are the advantages of stock over l/w?
Bellevue WA
90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
86 Porsche 951 - Track Toy