How Powerful a New Coil with a Factory Motorcraft Ignition Box?

[Fast79Chief]

Looking to replace my factory coil now that I stepped up to the new MSD distributor. I'm keeping the factory Motorcraft ignition box so I need to know how much coil output that box can handle?

If anybody has replaced their coil with a newer higher output unit, kept the factory 79 ignition box, and didn't burn out the box, let me know.'

Thanks a lot.

[Stuka]

The box has no impact on what coil you can use. The box just sends a signal to the coil. The coil is charged off a 12V feed.

You can go to a TFI style coil if the MSD distributer has the right style cap.

[Fast79Chief]

Ok Stuka ... I thought somebody had said I had to be careful not to "meltdown the box" with too much coil voltage. I'll be keeping with the stock location for the coil, so it will be a similar body style. The 'Blaster' coil is too expensive for my pocketbook ... got to find one with more output than stock for the same money. lol

[Stuka]

Doing a TFI ignition using the stock box is very common. It doubles the voltage output from the coil. Ford did this from the factory with the duraspark module. The box never sees any of that voltage. It just tells the field when to collapse which generates the spark.

[Fast79Chief]

Thanks Stuka!

[tgreese]

Well, it should be ok if you leave the factory ballast wire in place. The coil and ballast wire determine how much current the module must sink. Eliminate the ballast wire and run a low-resistance coil, and you will likely melt the module. But that has nothing to do with the distributor.

[Fast79Chief]

So if I dont change the factory wiring to the coil, will that allow the ballast you are talking about to remain in the loop? I plan on replacing the coil with a 35 or 45,000 output coil. What resistance coil should I look for so I do not cook the box?

Thanks guys.

[tgreese]

Yes, should be ok. Definitely leave the original coil wire in place.

Voltage is not relevant, resistance is. Typically the higher the voltage, the more turns on the primary and the higher the resistance. More resistance means lower current.

I'd just use the factory Ford Duraspark II coil. It's a hot coil, like the HEI coil, and the same EI design. I believe that people have had good results with that and not ruined their module.

Another possibility is to keep the factory coil and run the MSD module. That would give you a hotter spark than the hot coil would provide on its own.

[Fast79Chief]

I have the new MSD 8519 distributor in there now. NOT going to change out to Ford cap and rotor. Trying to avoid spending another 300.00 on MSD's box. That's the reason I left the factory box in place. I'll get a new 'barrel' shaped coil and call it good enough. Thanks to all for your help.

[Fast79Chief]

Found this Taylor Ford DuraSpark cannister coil on Summit website. I'll load the specs on it to see if it is OK as far as resistance goes.
Be back ...

Summit part # TAY-718205
Max Volt 45,000 V
Primary Resistance .700 ohms
Secondary Resistance 4.70K ohms
Inductance 8.00 mh
Peak Current 140 mA
Spark Duration 350 uS

NOTE: "If using this coil with a stock Duraspark ignition, a ballast resister must be used." Says the ad.

Could I use this coil with my factory coil wiring and factory Motorcraft box?