Cable size for battery in trunk
...also solder the terminals on to the cables. You can do this by melting solder in the terminals with a propane torch with the terminals clamped upside down in a vise, and then with the solder molten, pushing the cable in the molten solder and letting it harden. My buddies at MSD actually tested running grounds on engines with aluminum heads and gained 9 HP just by grounding each head to the chassis. This is because the spark takes place in the heads.