If a lighter weight flywheel is used, then less power will be taken from the engine to spin it, which means that more power can be delivered through the system and thereby increase the RPMs.
plus shifting in manual gear is easier The revs of the input shaft tend to fall just a little bit more quickly when the flywheel light weight and as a result this means that the transmission's synchronizers don't have to work so hard.
You can get your stock flywheel light weight