Ok so i picked up a used Rockford HE2 10" sub and a ported box for $60 bucks from a buddy of mine. I hooked it up to a 300 watt max/150 watt cont. @ 4ohm amplifier that i got at walmart. Now it seems to me that a 150 watt amp, hooked up with 8 gauge power/ground wires, shouldn't really drain THAT much on the alternator while the car is running. But from what i've seen so far, when sitting at an idle with some good hip-hop or rap going the needle will swing from 3/4 to a tick below half when the bass hits. This is with the car warmed up, in park, with the headlights on. Does this seem normal or is my car having a hard time keeping up?

you alt and battery are talking a beating....i would suggest an bigger (140 amp) alternator

Agree with Pat on this..sounds like your alternator isn't able to keep up. May be weak, or could be the drain is too quick.

Try upgrading your wiring. I would use 4/0 at least for wiring the system. Try doing the Big 3 to help your electrical system.

http://forums.caraudio.com/vb/showthread.php?t=124175

There'* a link for it.

Ok that'* what i thought it was. I cleaned all the + cable ends on the battery, they were pretty bad. I dont' know how the grounds are.. but the car will be sold before the end of the week so i'm not to worried about it. I think it'* got the 108 Amp alternator on it now according to the RPO list.

some amps draw more power to produce the same output as others that draw less.

Yes I know it sounds funny but its true.

I can run a LOT off my stock 105(or 110 dont remember)amp alt before I really start dimming.

big 3 seems to be a must for you.