80 feet of #2 has a resistance of .012 ohms and so a drop of 1.2 volts
at 100 amps. #2 with typical insulation is rated at 95 amps. Maybe you
are "intermittent duty"?

80 feet of #1 has a resistance of .0096 ohms, and so a drop of .96
volts at 100 amps. #1 is rated at 110 amps.