New cables and GOOD GROUNDing connections to the block and the firewall. Clean the oxidation off the firewall seal with good dielectric grease. I got 12 from 6 volts at my starter and what feels like 30 horses back. It's a new car! The previous owner asked me why his ex-Z was running so good. I let him know i replaced the ignition switch, then the coil, then the starter wires, and finally found the battery wires and grounding to be the big time fix.