a capacitor will NOT make-up for an alternator that isn't charging the way it should. even if the alternator were spinning @ the proper rpm, if the alternator doesn't have the output that would support a large stereo system, a capacitor will NOT help. a capacitor is placed into the system to help with transient response. that is why the pioneers of the use of them used them. not even an optima yellow top will 'save' you.

lightweight crank pullies can cause a problem with the overall balance of the rotating assembly.