New car manufacturers for sure don't run any heavier cable then necessary. The Ford Racing starter I'm using came with a 4awg cable - which I replaced with a 1awg from the trunk to the starter. The ground is the same 1awg and is fastened to the the bell housing near the starter with the frame and body separately grounded with woven straps and brass bolts - kinda overkill for a steel bodied car, but it was only a few bucks more to make sure.