Pertronix does list the requirements, in Ohms of resistance, for  their distributor pickups in the instructions. Any coil that meets the !.5 Ohms of resistance (I think) should be OK


  

Frank/Rebop

Bristol, In ( by Elkhart) 

But after about 1960 they stopped using an external ballast resistor and started using a resistor wire. I've has a Pertronix I in my 66 mustang using the stock resistor wire and stock coil for the past 20 years, it has worked flawlessly. My 57 I have a Pertronix II with an epoxy coil and no ballast resistor with no problems.

"There's nothing that says one has to use Flamethrower branded coils with the Ignitors (though I'm sure Pertronix would like that) there may be better choices out there." Tedster

My best friend has a 1964 Galaxy convertible.  We have been running a Pertronix I module with no external resistor and an Autozone resistor coil for two years,   

I'm figuring it simply has a larger number of turns in the primary winding is what I was getting at. Can you cut that one open? Is there actually a ballast inside those coils? I don't think there is. Maybe.

Anyhoo this question about the coil ohms comes up a lot, it seems like voodoo to a lot of folks. They seem to zero in on "whether it has a resistor" or not, when what they need to do is measure it, and make sure it is compatible with the rest of the ignition.

If they would study Ohm's Law a little bit, and understand the circuit better they can use just about whatever combination of mix and match scratch and dent parts they want and it will give good service. The key is to keep the current flow within specs.

There's nothing that says one has to use Flamethrower branded coils with the Ignitors (though I'm sure Pertronix would like that) there may be better choices out there. So long as the primary/secondary resistance is the similar, it should make absolutely no difference in the performance. I replaced the oil filled unit after it started leaking after several years with an epoxy filled unit.

There are currently no domestically produced ignition coils is my understanding, but I'm told that the Bosch Blue is an excellent unit, it is a 3.0 ohm coil made in Brazil or Mexico iirc.

When I mentioned using the same Ignitor I for 20 years with excellent service, maybe Pertronix has long since offshored production for those by now. I don't know.

Gene, thanks for the answer! My Daddy told me years ago about creating a spark gap to make Ford A-Models run, but he never told me how it was done. I remember asking him one time why it made them run better and he said he didn't know, it just did. The part about building up the voltage in the coil to create enough power to jump the gap makes perfect sense. I miss my Daddy, he's been gone 33 years now.

As a technical point, I hear people sometimes say a particular ignition coil "has an internal resistor". I'm not sure this is correct. I've never seen one. Maybe.

One Example - FORD DURASPARK I

____________________________

You cut the wire and strip the insulation so there is about an inch of bare wire exposed on both pieces. Tie the stripped wire into the button holes diagonal to one another so as to create a gap for the spark to jump. I've seen them placed on an individual plug wire to help an oil fouled single plug. 

I remember those demonstrations. I have a question though. How was the button installed to create the spark gap? I've tried to picture it in my mind, but it eludes me!

So, remember you old timers, the demonstration of the "Hot Spark Intensifier" at the county fair?
I'll bet the unit was nothing more than a coat  button and a few wires  inside that  box!!!! 
AH-HA!

"FREE SAMPLE"

I am running a Pertronix I with a Pertronix 1.5 Ohm coil with no resistor.  The only problem I have had has been with the Electronic Tach.  I had to add a 10 Ohm resistor to get the tach to read right.  Other than that, no problems.