Better damping (most likely?), higher acceptable rpm limit (not a rubber based damper!), SFI approved, considerably lighter (think lightened flywheel with $600 less labor! 2lb's can do alot!
), and atleast 20% less parasitic drag on the motor from the accessories...
...and ScottK. You are not running a damper; like Dan mentioned. Since the UR is just a UD Pulley (No Damper!) This is why it's so ultra light...
On weight...
A decent guestimate on weight would be ~1.5lbs. The stock one is ~3.5lbs.
