Trying to push 40 Amps through 160 feet of 8 gauge is a lot like filling a swimming pool with a garden hose.
Either RE- wire the panels in series strings, AND/Or upgrade the cable.
If you HAVE to run the panels all in parallel, you will need at least 2 gauge wire.
( I use 2 gauge welding lead for my 8 x 220 watt array, 65 foot distance x 2 conductors = 130 feet of 2 gauge.. mine run at 104 volts Open, 80 volts loaded. )
