Your amps are not 84% efficient...at least not at normal listening levels. Amplifiers are most efficient at max power, doesn't matter if it's a Class A or D. At lower volumes, where you're listening to music most of the time, most Class D amps will have the same efficiency as an AB. So unless you're blasting sine waves at full tilt; don't pay much attention to efficiency ratings. Think about all the people here who say they had to upgrade this & that to run their big Class D amp...a truly efficient system wouldn't require that.
You can run A LOT of power thru a stock charging system and there's really no need for 1/0 fire hose for power wire. Most street systems will need 4ga at the largest. This is b/c music is dynamic and the amp will not draw max current for any sustained time. Those times where the amp needs more power is handled by the capacitors inside the amp constantly discharging during music peaks and recharging afterwards. They call this 'ripple' and is another reason why adding a quality 1 farad capacitor to a system is never a bad idea as they smooth out power delivery to the amp.
I've owned a few Fords with stock electrical systems and never had major issues requiring an upgraded electrical system. I had a Mustang with a pair of Xtant amps and an UNDERDRIVE pulley - no problems. The lights dimmed at idle and perked up with revs regardless if the amps were on or off. No dimming while driving. I also owned a Thunderbird many moons ago with a SQ+ system. The sub amp was that big Eclipse dual mono thing (Class AB) running 2ohm stereo and the lights slightly dimmed only when I absolutely beat on the subs and it was winter so the blower motor & rear defroster were on. Stock alternator with a normal lead-acid battery and that car metered over 140dB.
Both those cars were set with an o-scope at 0dB overlap and had headroom galore. Both those cars were 'rated'
