The alternator I'm running is a 90 amp. In my youth I had an expensive stereo in the car and every time I would crank the system the lights would dim to the beat of the drums or base, I was running a 40amp then so I replaced it with the 90 amp to cure the problem and the alternator has just kind of ridden in the car since then. I figure if I'm going to do the electrical work around it would save me some money in the short term not buying a new alternator, plus the pulleys would need to be changed out as I have a March system on there now.