Originally Posted by KoolKarmaJoe

OK, bare with me, I'm a "driver" not so much a "gear head" so my observations are from that perspective. ACT HDSS Clutch, needs 300-500 miles breakin (not just highway miles; stop n go daily driving too). So far I only have 78 miles on it. The lighter ACT Streetlite Flywheel gives quicker revs, and upshifting is extremely fast & smooth. Quick downshifting I found is much smoother with double clutching/rev matching, & heel n toe driving method. Yesterday on my way to a "Z & Coffee Event" I got stuck in a backup on I-70, stop n go 5mph or less. It did get a little annoying with some clutch judder. It seemed to increase with each time I let out on clutch (about every 30-90 seconds as cars inched along). Once cleared and moving clutch settled down & was fine during normal stop light/intersection stops. Again, remember I have not reached the full BREAKIN PERIOD as of yet! The lighter flywheel has less mass therefore as quickly as it revs up, it also revs down. You will notice that you may have to rev a little higher to start from a stopped position on a incline/hill. But I've gotten much better with it with practice. In a way, you will have to learn your clutch style over again when changing from OEM setup, but thats not bad, its no different than getting use to clutch feel in a different car than your are use to driving. Definitely change transmission gear oil to the MOTUL Gear Oil (ZSpeed 4qts=$74.00). Cheaper, old gear oil may result in louder chatter noise. There is a YouTube by ZSpeed where Joe demonstrates flywheel chatter from a 19lb solid flywheel. Though he doesn't mention brand name, I DO NOT THINK it is a ACT 19lb flywheel, because no-way does the ACT HDSS Clutch Kit & ACT 19lb Streetlite Flywheel sound that loud on my car whether it be cold/hot start, or A/C on or off, clutch in or out at idle.
As I break-in this system I will post updates and will closely monitor if there is any change in level of noise chatter, grabbing, slipping etc. It's still new setup (only 78 miles on it), and currently I am very pleased with it.
If you plan to eventually go FI, you will have to upgrade from OEM Clutch.