Trust the Japanese to know about this :-) The heavy flywheels have more inertia so when you drop the clutch they aren't going to slow down as much. If you want a car for auto crossing then a lightened flywheel is what you want for quicker acceleration out of corners. All the heavy duty clutch companies here sell their clutches as a set with a heavy (heavier than stock) flywheel. If you get a lightened flywheel and later on you need a OS Giken twin or triple plate clutch, your lightened flywheel won't work with the OS Giken clutch.
