OK, let me go drink at least two 6-packs, to prepare for the whizzing contest!
I prefer to deal with real-world experiences, rather than delve into mind-numbing theoretical discussions. A piece of #1 or #0 welder cable, with its hundreds of hair-fine strands will provide all the current-carrying capacity any 6 volt starter will ever need. As long as the terminal ends are soldered on for minimal voltage drop, and kept tight, there should be absolutely no need for mega-cables.
The practical way to evaluate a starting system's performance is a "series resistance test" where the voltage drop is monitored at each cable and connection from the battery to the starter, and back to the battery while cranking is in process. On the hot side, the allowable voltage drop on a 6V system is 0.1 volt per connection point and ZERO voltage drop from one end of the cable to the other. Ditto on the ground side. 12 volt systems can tolerate twice the drop at connections,(0.2V) still with little or no drop from one end of a conductor to the other.
I ran an 8D series 12 volt battery that weighed over 120 pounds in my road service truck, with 2-0 welder cable run to both ends of the truck to plug-in booster cable connectors, with the same type of cable in 25-foot lengths to my jumper cable clamps, and boosted Cummins, Cat, and Detroit engines with them with no problems. I also had a 200-amp brushless alternator on the service rig. 4-0 cables- - - - they're totally unnecessary, even for jump-starting a bulldozer!
Jerry
