If you are still running carbs and nothing real power hungry in the zed, stock alternator should be fine... I had to upgrade to a 280ZX one now because of the ECU, fuel pumps, thermo fan, injectors, sensors and everything else that sucks power. Stock 240Z alternator couldn't cope with all that load. Since I installed it, I can tell the difference! Everything runs well when it receives 14 volts instead of 12!