I have been trying to decide whether to continue to use the internal-resistor coil as I make the switch to pertronix, or instead to swap in one of my other external-resistance coils. The instructions state that I can use any coil with an internal resistance of 1.5-3.5 ohms, and/or that total primary resistance including external resistor is not to exceed 3.5 ohms. My internally resisted coil is in the accepted range, but so are the 1.5-ohm point-type coils I have. I suspect it will work fine with either.

Curiosity has led me to try to determine what the intended application was for the internally resisted coil. The only thing I’ve been able to nail it down to is a late 60s Opel Kadett! In fact, the only factory applications I’ve found for internally-resisted coils are 4-cyl European cars.

I have 3 such coils in my possession. All 3 have approximately 3.0 ohms primary and 9500 ohms secondary. I have 4 external-resistor coils, including an original mustard top, all of which have about 1.5 ohms primary and 7700-8700 ohms secondary. I know nothing about the performance properties of these coils besides their resistances. It has me wondering whether my points troubles were caused by incompatibility between the coil and condensers, knowing the coil was probably intended for a 4-cyl and the condenser for an 8-cyl. Any ideas whether this could be the case?

Regardless, I’m probably going to go with one of my 1.5 ohm coils and not use a resistor with pertronix.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

I don’t believe the condensers of years past would know the difference other than the possibility that 1/2 the operations would keep it cooler on a 4 to an 8 and 1/3 on a 6 to an 8. In all the years owning a points automobile engine I only had one condenser fail and it was a combo unit it on a 1973 Monte Carlo. As stated prior I have used a Pertronics coil AND a stock 56 ballast resistor for 9 years without fail. 

56 Vic, B'Ville 200 MPH Club Member, So Cal.

More than likely you will be ok using the onboard resistor, it that's what you wish to do, only IF the coil isn't too low in resistance. If the coil is one with a low primary resistance, then the onboard resistor will run too hot.   For example, the Ford yellow top coil should be used with a 1.5 ohm resistor as the two components establish the correct total circuit resistance.  By eliminating the resistor, a yellow top coil would run much too hot.    Pertronix makes a 1.5 ohm coil, among others, which would be totally  compatible with the Pertronix unit in the distributor and can run with no resistor.  By eliminating the resistor, the spark energy will be greatly increased and the Pertronix coil is designed and proven to function in this combination.  Trying to mix and match components could very well cause either the coil or resistor to run too hot and fail.  Also, I agree with the above post that a condenser doesn't know weather it's used with a 4, 6 or 8 cylinder engine. You probably have one of the numerous poor quality condensers now available.  

64F100 57FAIRLANE500

Ford Dearborn, are you saying that a conventional (not pertronix-brand) coil, such as the stock Ford yellow-top, will not work with the pertronix ignitor module unless the system has a resistor? I have the understanding that any coil having 1.5-3.5 ohms primary resistance will work with the pertronix.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

I have one engine running a stock mustard top coil with a pertronix.  You need the external ballast resister to cut the voltage down from 12V to about 8V as the factory designed it or the coil will overheat and burn out. The Pertronix is best run on 12V and thats why they recommend splicing the hot ( RED ) wire for the unit into the 12V line before the resistor.

I've always thought of the Pertronix as a switching device like a set of points.  The yellow-top coil is not truly a 12V coil. It operates at 6-7 volts accomplished by the additional 1.5 ohm resistor.  When cranking, the resistor is bypassed for ease of starting only.  Eliminating the 6V drop across the resistor would put full battery voltage across the coil when the points close and since the Pertronix is taking the place of the points, it should have the same effect on the circuit.  This would also double the current and that will produce  a very rapid rise time for greater saturation  producing a much hotter spark - the beauty of Pertronix.  The current of the yellow top coil is kept in check by the 1.5 ohm resistor. With out is, the current doubles. So, the 1.5 ohm coil would work if the resistor is kept in the circuit, IMO.   If the Pertronix has a current limiting feature at some threshold then I'm not aware of it and besides, that would defeat the purpose of developing a modern hot ignition.  The current is not straight forward because there are other things going on like dwell time and inductance.  Never the less, the book states 4.3 amps with the engine stopped and 2.5 amps idling in the primary circuit.  Without the resistor, this current would effectively double but not for long.  Maybe a Pertronix instruction sheet would address this?   

64F100 57FAIRLANE500

57RancheroJim you pulled the trigger before I did. Well said in a few words.............

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FORD DEARBORN
You provide great technical info which is right on, I try to keep mine short and simple because I hate typing.
I always wondered why they never built a true 12V coil, maybe they has so many 6V coils in stock it was cheaper to just add a resistor LOL

Manufacturers needed to lower the voltage and added the resister because 12-14.5 volts burned up the points! The first car I added 12 volts and a V8 to was a 53 GM car and I burned up the points in 5 miles. Because of coil heat I bought the Pertronix coil and kept the stock ballast resister after a call to them. They said either way and like others have said not quite as high of a spark under driving circumstances but with the bypass a hotter starting spark just like the stock points set up. It’s choice like they said.

To me the advantage was no more condenser failures or point maintenance.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Interesting. So, reading between the lines, you (both) are implying that the 1.5 ohm coil marketed by Pertronix is designed for the doubled current afforded by losing the resistor (total primary resistance of 1.5 instead of 3.0) so both it and the Ignitor switching module can handle it. Meanwhile, stock point-type coils are not designed for the extra current and would consequently live shortened lives, even though the ignitor itself would still be fine. Am I understanding you correctly?

Where my confusion comes in is that the guidance from the instructions seems to go against that. Here is a photo of the instructions included with my 1281 kit. As I read it, any coil or coil+resistor combo is fine provided that, for a V8, total primary resistance is 1.5-3.5 ohms and 12V is supplied to the ignitor module itself.

Seems like using an internally-resisted coil, or a stock coil+resistor, would be “safer” but may reduce spark energy as mentioned above. For my street-driven car I’m not sure that I’d ever know the difference. I just figured if Pertronix recommends not using a resistor, I’d go with their recommendation.

DryLakes, you posted while I was writing. It does seem like a matter of preference as you say, and like you I am just looking for reduced maintenance and reliable operation. I hope I can be one to say “ten years with no trouble!”

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive