[indymachinist]

Grounding the battery to the frame, then the starter/engine block to the frame is the way to go. Consider how much metal is in your frame. Now consider even a large battery cable running the full distance from front to back. You need to consider voltage drop here. The frame will have less of it than the cable.

Actually making proper grounds is critical here. Clean metal, good quality star washers, and corrosion protection.