I was jus wondering if anyone knows what size alt the 03 SS comes with looking to add subs and amp and was wondering if alt upgrade is needed thanks

 

The stock alternator should work fine, I've had a few cars over the years with one at 2000 watts and 2x12inch subs and never worried about the alternator putting out enough juice. The one thing you will notice is that the lights will dim when the bass is pushed hard. You can buy parts to solve this without changing the alternator. Your best bet would be to check in with a stereo installation store and see what they recommend for regulating the power for the system so that the lights don't dim.

I had one system that would make the hair on my head move with every beat lol, it's a wonder I still have hearing

 

The alternator will be fine. Do the big 3 wire upgrade and you should be fine.

 

You could always add another battery as well. I did that and it seems to help me. Defiantly do the big three though with 1/0 gauge wire.