What is the best material for refilling a dual mass flywheel? I realize this is more C4 LTx related than F-body so my apologies. But what’s the stuff they put in them from the factory and what would be better? Sure looks like plain ol black grease to me.

Besides additional weight, why aren't these flywheels more popular? Seems like they would cushion the initial shock some on launch and smooth out the engine during normal daily driving. GM uses them to tone down the ZF trans noise.

 

Not sure what is in there, but I will definitely say the ZF6 is much louder with a regular flywheel. Recently did an engine swap in a '94 Vette & was surprised how loud that trans is.

 

couple reasons-
Unless you balance both parts of the flywheel seperately, and neutral, and internally balance the motor the motor's balance will shift. I am sure there are some related harmonics that a dualmass flywheel could cause.
Also, as you said it WEIGHT. that thing is a hauss, and the last thing you want spinning is more weight.