i have a RF power 1500.1 that is sheeted at 1698 watts, and i have a RF power 360.2 that is sheeted at 482 watts. those are RMS numbers. i have FRPP underdrives, a stinger deep cycle in the trunk, and stock alternator at 130 amps. i have no problems at all. when i'm at idle, and pounding it, i do see the autometer gauge i have installed bounce from >14 to around 12 volts. but its an instantaneous thing. even at night with the lights on, its aroudn 13 volts or so. the underdrive pulley is not that much larger than the stock pulley, they make most of it up on the crank and water pump. there should be no worries with them.