depends on the amp you select. 4 ga is good for about 1200w. If you're actually planning to run 2000w you'll need 1/0. you could be looking at an alternator upgrade, too.
I agree and second that! I would just go with 0 guage regaurdless becaue it isn't that expensive for big wire. Small wire could melt or couse a fire in the vehicle. Especially at 2000W RMS!! I always use big wire for safety, but mostly because I don't care about the extra cost, its not much. Just my opinion!
Just my opinion!