Can my alternator handle the system I'm about to put in?

using 1/0 for the big three is about more than just the amps it will carry, the larger wire will have less resistance with the juice flowing. so it will actually help a bit.

It might make a tiny difference, but at 80 amps the voltage isn't going to drop that much in that short of wire either way. Now if it was a 320 amp alt. then you would be looking at 4x the voltage drop in the same length of wire, which may come up to be a more noticable number.

Edit: Just for piece of mind I calculated it out. In a 4 foot run of 4 gauge copper wire with 80 amps of current the voltage will drop .07952V, and that is if he removes the original wire and only uses 4 gauge. With a 4 ft run of 0 gauge copper wire with 80 amps of current the voltage will drop .031456V.

This is a great site to figure this type of information out, so everyone can do their own calculations. American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies . The formula for voltage drop across a resistor (wire) is pretty easy. Current x Resistance (must be calculated using chart depending on length of wire)=Voltage Drop. Class is dismissed.