Correct internal or external coil for pertronix points eliminater

Mike69cuda said
The voltage does not strictly depend on the coil. The formula for the coil voltage is V = L x di/dt.
The voltage is equal to the inductance of the coil times the speed of the current change. So the voltage output of the coil theoretically can depend of how fast the current is switched off. This can be faster with an electronic ignition. The inductance & turns ratio of the coil also figure into the calculation.

The above is an extremely simplified explanation of how things work. The coil and the ECU can both have an effect on spark voltage. However there are a lot of other factors. In reality, the gap size of the spark plug limits the high voltage in operation. When the spark plug breaks down, the high voltage goes away.

The moral to the story is that car ignitions are designed as a “system” and using them as designed will likely give you the best results.

When manufacturers advertise specs for their parts, they generally describe the conditions that are most favorable for their parts. This is usually a theoretical or “best case” situation which may not be practical in real life. So if they are comparing the highest possible voltage that can be generated by their ignition to a car with worn out points, they may not be lying, but they are not really telling the truth.

Agreed!!!
Fortunately I’ve never used one or purchased one and have only used points and I think a few hei in later 70s 80s type gm cars. So this was a mystery to me when I did the tune, heck I didn’t know what it was till I noticed and the dead Cylinder and what a debacle that was, took me to a while to figure out that the magnet fell off the rotor magnet cover.

tested wires and plugs with ohm meter and switched two rotors and caps and was ready to buy a reman dizzy with points when I noticed a magnet missing and bam problem solved. I think it’s wired pos neg to coil and pos still going to ballast so OEM setup, but other then ease of cleaning and or adjusting points I see $120 dollars well spent in other areas. I would definitely not buy this setup as points have been good to me in 25+ years of working on Oldsmobiles/GMs and Mopars