That should work. You usually buy caps at 1 farad per 1,000 watts. As to what would happen to the system... if you haven't upgraded your alternator and/or battery than probably not a ton. If you have then you'd probably notice a diff. on very hard/low bass hits that require extra large amounts of power. The cap would stiffen the power going to your amp, because it supply's that extra power at certain times that the battery can't get to the amp in time.