"Presumably you know ohms law, just calculate the value to give the 8 volts after starting. "

That will vary with RPM. It does not only because of more sparks per second, but with cam overlap the effective compression ratio changes. More atmosphere in there means a higher dielectric strength so it needs more firing voltage. That will change the current load on the primary and thus if not a solid voltage of course it will vary. the values they chose for the ballast kinda split the difference. That's why when you put a hot cam in a car you also beef up the ignition system to supply a higher voltage. You usually do the cam for more high end and it will still need enough firing voltage up there.

Yes, I am car people and from the old days. At my Uncle's funeral the picture of his car was bigger than the picture of him.

And that is the way he would have wanted it.

We never looked at any book to setup an engine. There was a 1957 Chevy that would pull the front wheels up in second gear, up to 110 MPH, and there was my cousin's 442 that was made into a 642 with three deuces and Edelbrock which ripped the front bolts out of the seat. Can you imagine that ? Your car is rolling down the road and you are laying down and kinda stuck... I would have liked to have a video of that but not actually be there... He lived though, it took a motorcycle to kill him. Well it was his fault I have to admit. And then there was my 1970 Toronado that ripped the asphalt up off the street, and this other car I forgot what it was exactly but I remember I bought it off of a guy named Dwayne but the title was made out to Dawne. I never got the title in my name, I had spare plates all over the place. Why bother ? When I bought it I told him "OK, just sign the title Dawne". LOL My other Uncle was a notary public and he flipped cars, alot of them. If you have more that like 12 in a year you are supposed to have a dealer's license in this state, but they didn't go in his name. People sold him a car and just signed the title, when someone bought it he just put their name on it and notarized it. Everything he touched turned to gold. And that is only a small tip of the iceberg.

So when it comes to old cars, well...