Electrical: Which coil/resistor/condenser for 6V to 12 V conversion - 1937 President 8

[garyash]

Rather than hijack Jackb's current thread on coils, I'll start a new one. I'm building a 1937 President straight 8 (250 cu in) engine for my Indy car replica. I had the generator rewound for 12 volts and the starter rebuilt. Now I'm ready for ignition components. The original Delco-Remy 662M distributor has dual points, but it's just a standard mechanical distributor otherwise. I need to pick a good coil, add a ballast resistor (I think), and mount a capacitor on the distributor. I'll use copper core wires as there won't be a radio. Engine redline is about 4200-4400 rpm. Except for instruments, lights, and electric radiator fan, there are no other electrical accessories. So,

Which coil do I use? Summit Racing lists 3,000 coils. I just want a good one with hot spark in a black case but without internal ballast resistor.

Which ballast resistor is needed? I think it should be about 1.3 ohms, but educate me. There is no "pink wire". I think it will start OK without bypassing the resistor when cranking.

What value condenser/capacitor is needed? I think 0.2-0.25 microfarads is the common one. Any reason for different values? I don't actually see microfarad values for ignition condensers on any sellers' websites, so maybe it doesn't make much difference as long as they are good for 400-600 volts. The differences seem to be in how they are mounted.

Which spark plugs to use? They need to be 18 mm threads, so that limits the choices. Originals were Champion 7-A or 13 for hard driving , 8-A for milder use.

Remember, this is supposed to look 1932-ish, so I don't want to go with electronic gizmos. And, I won't really be running in the Indy 500. I'm hoping to get close to 190-200 hp using four EX-23 carbs.

[gordr]

Well, presumably you want a coil with screw terminals, since push-ons aren't era-appropriate. Why not just use a standard coil and condenser as used in say, a 1960 Lark VIII? Now, finding a ballast resistor block with screw terminals may be a little harder. I think the mid-'50's Studebakers that used a discrete ballast resistor had push-on terminals on them.

[RadioRoy]

What value condenser/capacitor is needed? I think 0.2-0.25 microfarads is the common one. Any reason for different values? I don't actually see microfarad values for ignition condensers on any sellers' websites, so maybe it doesn't make much difference as long as they are good for 400-600 volts. The differences seem to be in how they are mounted.

Unless I am misunderstanding what you mean, that capacitor/condenser is for radio interference. You should not need it at all.

As far as the coil and ballast, when converting from 6 volts to 12 volts, I always look at 1956. That was the very first year for Studebaker 12 volt systems, and my assumption is that those components would look more like the 6 volt ones, appearance-wise, than any subsequent year.

[(S)]

I'm currently re- wiring a 1956 Hawk. It has a white ceramic resistor with screw terminals. I would use a similar resistor and just hide it behind the head or even inside the car......... I thought the old 1930's used something similar, just an older design/of the era. As for the rest of the parts I don't think they care unless they are too 'hot' and burn up plugs, or too 'cold' and don't burn proper.

https://www.ebay.com/itm/BALLAST-RESISTOR-FORD-1940-1941-1942-1946-1947-1948-MERCURY-1946-1947-1948/333099535753?epid=169274932&hash=item4d8e478d89:g:FbEAAOSwq4xcerBi:sc:USPSFirstClass!98248!US!-1

[garyash]

Roy, I think the ignition condenser is required at the distributor. It prevents the points from burning when they open and the coil is discharging. Too much capacitance and tungsten moves from the positive side to the negative point. Too little, and a pit develops on the negative side and a point grows on the positive side. So, I guess I pick a condenser and see where the point and pit develop. With luck, no point, no pit!

For plugs, it’s looking like D14 or D16 Champions or equal/better, without resistors built in, same as for old tractors. I’ll be making lots of RFI/EMI, but not many folks have their AM radios on anymore.

[RadioRoy]

Gary, is the ignition condenser not inside the distributor in a 37? I am only familiar with postwar cars and the ones I have seen all have the condenser inside the distributor alongside the points.

[garyash]

With two sets of points inside, there apparently wasn't room in there for a condenser, too. I had to 3D print a new feedthrough terminal for the side and turn a brass stud to go in it.

[RadioRoy]

Got it. Thanks.

[Trikebldr]

The coil and condenser are matched for their values which constitute a tuned circuit. Mismatching them is what does cause bad pitting of the points. Also, when you add in the resistor, that affects the tuned circuit between the coil and condenser (basic electronics!).
The best thing to do is look back at just about an make of car (Ford, Chevy, Chrysler) for a coil AND resistor that give you the appearance you are hoping for and order the three of them for the same car. This way, all that matching work has been done long ago.
I know Chrysler stuck with using the usual black-can coils with the 3" long white ceramic resistors with screw terminals on each end and their condensers were usually inside the distributor until they used dual point ones on the early 383's. It really doesn't matter where you put that condenser, inside or out of the distributor.
Ford also used very similar coils/condensers/resistors.