1: Stiffer motor and tranny mounts directs more power instead of having to "balance" the vibrations since softer mounts dampens the vibrations coming through the engine to the drive train. So with stiffer mounts its said that the engine will respond alot better with the drivetrain, some what better "engine response". But you'll have more vibrations coming out from the ening with stiff mounts, solution= HPI or 5Zigen engine torque damper.
exe=
HPI torque damper (red looking stick near the exhaust manifold)
HPI's site
heh, they also make carbon fiber doors for silvia's/240sx's
2: Having a lighter fly wheel helps the car rev up faster. You could also get light weight gear pullys, or get both and you'll really notice how you car revs. Usually don't go lower then 11 pounds unless you got more then 300 HP, its kind of over kill. Lighter flywheels don't make power, they free up power, understand that. People keep thinking it makes power. Same thing with light weight gear pullys.
What level is the cluth rated at? Having too high of a clutch that can hold more power then your putting out will put alot of stress on your drivetrain; especially the tranny. Turbo magazines recommend using a low level clutch thats in your power range. Or you can learn the hardways like my honda's friends and either get your tranny rebuilt 5 months from install or get a new one.