What is an acceptable voltage drop?

[ultimate157 5,000+ posts]

Went and reground the metal where my ground was and also added another 0 gauge ground, played the same song (soul survivor) and voltage dropped to 13.8v @ idle and 14.1v @ 1200 rpm:veryhapp:

2 runs of 0 gauge from front to rear battery bank. Then 2 0 gauge grounds from bank to chassis(rear seat mounting studs).

Well theres your problem. With an electrical system that beefy, you really should run dedicated grounds back to the front and tie in to the battery.