what amps, what subs? saying 3 amp is arbitrary, you could have 3 flea market "1000w" amps that pull 20amps on a good day, or you could have 3 orion 2100 hcca that would crush a stock electrical system, pulling 875-100amps each. There's several companies that make aftermarket alternators, If you want big and custom there's plenty of those. One thing with an alternator, if you're overstressing it, you'll know, I killed my OEM alternator when it was barely 3 months old, and I was overstressing it much, stock was 105A, on an onry day my system pulls 145amps, guess I had a few too many onry days. Give alterstart a call and see what they can do for you, that's what I'm running in my car, and it's been two year with no troubles, well aside from my car falling apart because of the bass. Also you might want to look into getting a batcap(or another stiffening device) and/or at least upgrading your stock battery(if you haven't already)