[RICK LAKE]

NG8264723 Chris You are leaving out a couple off other loads on the system possibly. Does the car have electric fuel pump??? 6-10 amps. MSD ignition system??? 4-12 amps. Your cooling fan 8-20 amps. Lights 2-10 amps. If you are running a smaller bottom pulley than 5" the system is under drivin. The Alt is not spinning fast enought to power all these curcuits without draining the battery at idle. Size of battery also comes into this draining also and health of battery. CCA I like are in the 800-1000 cca. This gives the systems alot longer time to kill the battery and have the car not start. If running a MSD system, when the battery gets down to 10.2-10.4 volts it will not have enough voltage for the ignition to start the car.
The other issue could be the output on the Alt is not what is said to be on the case. Have to remember that the rating is for MAX ampage, but it can't run this way all the time. If the amp rating on the Alt is 70, it may only maintain a 62-64 amp max without burning up the alt. At idle you may only have a 30-35 amp output and this is not enough. The battery is suppling the extra amps for the car to be running at low rpoms. I have had the problems you are going through. You might want to have the battery tested for CCA and health of it. Go to a good place for a battery check not Pepboys, autozone or Sears. They all have questionable machines for testing and failing batterys. See if there is a higher CCA battery for the car that is the same size as what you have now. I run more electrical than a 70 Alt can handle with fuel pumps (2) fans coolant (3) ignition system, FI system. and Blowers (3). I also have an under driven pulley on the bottom of the motor. Have gone to a 100amp PAPreformance setup and a Voltage meter for the electrical system. I wouldn't recomemend running a higher alt rated than 70 with an amp meter in the car. At this time all volt meters are different color and don't match the original gauges of SW or Smith in the car. If the color bothers you, remove the gauge face and paint it black. You will need to rehook the wiring from the gauge. The problem is cooking the insolators on the gauge and smoking the whole dash wiring harness. Talk to Kirkham about changing to a larger charging system. Rick L.