Is running 8 AWG power to a MRP-M850 a sin?

[Atimm693 10+ year member]

That amp will draw more current than 8awg wire can handle, which not only will "starve" your amp but can also set your car on fire because the wire would get so hot.

The fuse would blow before the wire would heat up.

To calculate amperage in a car you take watts/volts.

850/14=80 amps at 75% efficiency.

4g for now, 1/0 if you plan on upgrading.