I think it is the flywheel then. What I have heard previously is something about Wira 1.5 changing into the clutch from Wira 1.6 which also requires something like modifying the clutch cover. Sorry, what I heard that time is in cantonese not in english, so I wasn't so sure what it meant.
Then I guess those who use those heavy racing clutch on street cars is rather pointless. No point in getting those Ogura Super Single Clutch
I've also heard about making the car easier to accelerate during uphill if 4G15 is using the clutch from 4G92.
upgrade bigger clutch=adding more surface friction..more grip...
and also directly adding rotational weight which is more inertia for engine carrying rpm while moving...
yep...no point using race clutch when stock clutch will be just fine for daily usage....unless the car also going to trackday/dragstrip