the stock unit is a dual mass type, aftermarket ones are not. As such, aftermarket ones transmit noise that the stock unit insulates. This happens at low revs only (from about 1000 rpm to about 2000 rpm or so. You can read about them in very general terms here:

http://www.high-impact.net/transmiss...svsSolidFW.htm

that being said, the cost and benefit of the lightweight flywheel (in terms of better engine response, quicker revs, particularly on a naturally aspirated car) for many of us outweigh the increased noise at very low revs

 

I am in the same boat as far as my flywheel worn out. I want the Nismo flywheel/clutch. I was looking on the Nismo parts list and it states that for the clutch it requires new return spring for 06 hi-rev engine. Could someone tell me what that means please.