I couldn't quickly find any specific electrical data on the Pro Comp PC-91 coil - but the lit does say that it's for use with CDI systems. The Capacitive Discharge Ignitions generally "like" coils with pretty low primary resistance because they are using the coil for a step-up transformer - not to provide an inductive surge.

You will probably need a pretty high resistance ballast resistor to keep the amp load down on the points - if you are retaining the points system. The sum of resistance that was listed above is 3.0 ohms or there about - and you are going to need to find a resistor that sums with the Pro Comp coil to provide something near to that or slightly less.

 
 Steve Metzger       Tucson, Arizona

Some aftermarket coils do not require a resistor.


Lawrenceville, GA

By Pete's reply, Ford's O. E. M. is using a resistor of slightly less resistance than the coil primary; this would give the coil a little more "omph" for a somewhat stronger spark.

Don't forget that you can use the "I" (ignition) contact on the four-post ford starter solenoid to 'bypass' the ignition resistor directly to the coil 'hot' during cranking for a stronger spark to start.  The 3-post solenoid does not have this provision.

Regards,  JLB

55 Ford Crown Victoria Steel Top

The 57 Ford shop manual shows 1.40 to 1.54 Ohlms @ 75 degree F and Primary resistance 1.30 to 1.40 and Secondary 8000 to 8800 @ 75 degrees F.  Pete

Thanks for the info. I am putting on a 12 volt Procomp 91 high intensity coil. Would I have to contack them to find out what the primary resistance is on that particular coil?

Old Y Block

I don't mean to 'pull your chain', but, the answer is yes: It could be any size in ohms in that range and is dependent on the coil with which it's used.   To use a 6V coil on a 12 V system the resistor should be the same ohms as the coil primary.

I do not 'know' the O. E. M. size.

Regards,   JLB

55 Ford Crown Victoria Steel Top

Could anyone tell me what is the proper resistance for a coil resistor for a 1957 Ford V8? I've seen everything from .8 ohm to 1.8 ohm. Thank you.