New coil, new distributor, two ballasts?

-
Ben A...

Ben A...

Well-Known Member
Joined
Jan 14, 2020
Messages
147
Reaction score
53
Location
Los Angeles
Hey there,
I want to install an MSD Blaster 2 coil, and a Proform Electronic Distributor.

Both come with their own ballast resistor.
The MSD coil has an 0.8ohm resistor and the Proform distributor has 1.25ohm resistor.

Which one do I use? They're both wired to the positive side of the coil so I assume I just use one... My hunch is to use the one equipped with the distributor.

Thank you for any help.
 
Dana67Dart said:
How is each wired per the supplier
Click to expand...
This is what I have for wiring diagrams. Does this help?
From everything I've read online it's advisable to run the MSD coil and ballast with this electronic distributor, even though the MSD guide just mentions it for points ignition here... Just not sure which ballast.

IMG_7066.JPG


IMG_7067.JPG
 
My usual answer is to go with the resistor's main purpose.
It's there to control the primary current through the coil when the engine is running.
A little more explanation here on pages 4-5: Ignition System Analysis (Session 259) from the Master Technician's Service Conference
During starting the battery at best is at 11 volts, and could be down close to 9 Volts, so the resistor is bypassed.

I'd say use the one that came with the Blaster 2 since it probably matched for it.
When the Blaster 2 is used with an MSD ignition, the resistor is bypassed since the MSD box discharges into the coil primary.

I'd bet if you measured the Blaster's resistance and added the .8 ohms it would be close to the factroy coil plus the factory ballast's resistance (.5 to .7 IIRC)

I assume here you are using a Chrysler box or similar replacement.
If you are using the original '73 ignition box, there was a second resistor just for the box's current control. It was 5 ohms.
 
Use the appropriate resistor with the ignition that calls for. Was this a trick question?
 
I've got a factory orange box setup with an MSD Blaster 2. Mine has the factory supplied ballast resistor, and being that it's limiting the coil on the positive side by a specific impedance and limiting current flow to the coil through the ignition unit, I would use the one supplied in the ProForm kit. A little higher impedance won't hurt the coil but a little lower impedance may not work too well for very long with the ignition box.
 
Mattax said:
My usual answer is to go with the resistor's main purpose.
It's there to control the primary current through the coil when the engine is running.
A little more explanation here on pages 4-5: Ignition System Analysis (Session 259) from the Master Technician's Service Conference
During starting the battery at best is at 11 volts, and could be down close to 9 Volts, so the resistor is bypassed.

I'd say use the one that came with the Blaster 2 since it probably matched for it.
When the Blaster 2 is used with an MSD ignition, the resistor is bypassed since the MSD box discharges into the coil primary.

I'd bet if you measured the Blaster's resistance and added the .8 ohms it would be close to the factroy coil plus the factory ballast's resistance (.5 to .7 IIRC)

I assume here you are using a Chrysler box or similar replacement.
If you are using the original '73 ignition box, there was a second resistor just for the box's current control. It was 5 ohms.
Click to expand...

Solid explanation. I'll check into this service guide. I can solder and shrink tube like a champ, but I really know nothing about electrical. Ohms or anything. Thank you for this.
 
Last edited:
Garrett Ellison said:
I've got a factory orange box setup with an MSD Blaster 2. Mine has the factory supplied ballast resistor, and being that it's limiting the coil on the positive side by a specific impedance and limiting current flow to the coil through the ignition unit, I would use the one supplied in the ProForm kit. A little higher impedance won't hurt the coil but a little lower impedance may not work too well for very long with the ignition box.
Click to expand...
Uh oh, that's ALSO a good explanation... but I believe it differs from the others...
The Proform distributor comes with it's own orange box? :/

It wouldn't make sense to use both I imagine?
 
Garrett Ellison said:
I've got a factory orange box setup with an MSD Blaster 2. Mine has the factory supplied ballast resistor, and being that it's limiting the coil on the positive side by a specific impedance and limiting current flow to the coil through the ignition unit, I would use the one supplied in the ProForm kit. A little higher impedance won't hurt the coil but a little lower impedance may not work too well for very long with the ignition box.
Click to expand...
I thought the newer '4 pin' boxes have their own current control internally - blue wire in the paper diagram above. And the black wire I assume is simply a open/close switch. I would *think* it could handle most any reasonable current through the coil. No?
 
Last edited:
Does proform sell their own coil? Maybe its an even lower resistance coil than the Blaster 2 and so they have a higher resistance ballast??

FWIW the Engine book lists 0.5 ohms as the most common recommendation for general use production and chrome boxes. But as high as .8 ohms for use with Accel's Supercoil.
 
Mattax said:
Does proform sell their own coil? Maybe its an even lower resistance coil than the Blaster 2 and so they have a higher resistance ballast??

FWIW the Engine book lists 0.5 ohms as the most common recommendation for general use production and chrome boxes. But as high as .8 ohms for use with Accel's Supercoil.
Click to expand...


Yes, they do! Good point.
Distributor Ignition Coils | Ford, GM and Universal
 
Good point Mattax. I somehow overlooked the internal limiter in four pin vs. the 5 pin with the second ballast strip. The MSD ballast would be my choice, but I’m able to run a .045 plug gap with my present setup so I’m not going to complain. I plan on a switch to a chrome box when I toast the orange box.
 
67Dart273 said:
Actually Rob I'd lean towards the resistor goes with the coil
Click to expand...

That's kinda what I meant. I think whichever kit he chooses would say which resistor to use with which coil......but again, I assume nothing. LMAO
 
"Back in the day" There were a couple of coils that required TWO resistors in series. One was the big' ol Mallory rectangular coil. You got a resistor with the coil and ADDED it to the one in the vehicle. I think one of the Accel coils was same way.
 
67Dart273 said:
"Back in the day" There were a couple of coils that required TWO resistors in series. One was the big' ol Mallory rectangular coil. You got a resistor with the coil and ADDED it to the one in the vehicle. I think one of the Accel coils was same way.
Click to expand...

I've seen one of the Mallorys in action, probably about 1981. lol
 
GREEN DART 5 said:
What coil..?
Check out post #28.
Click to expand...
Great post thank you for finding this.

So the MSD Blaster 2 coil is spec'd at .7 ohms (tho I've read it goes up to 1ohm).
With the distributor supplied 1.25ohm resistor that puts me at a total 1.95-2.25ohms. Which leaves me approximately around 6 amps? Too high I assume, but I cant find specs for the orange box.
 
Those were just round number examples he was giving to explain why the coil and resistor go together.

From the electrical section, '73 Dodge FSM.
upload_2020-2-7_11-20-12.png


Later in that thread they discuss flyback voltage. But unless I misunderstood, the thing that will overheat is the coil. The switching should have low resistance and not be a factor. On the top of a genuine Chrysler ECU is a big transistor that does get hot. Its possible that transistor might get even hotter with more current. New ones use a small transistor inside - often without a heat sink. Good luck on finding any honest info about what they can tolerate....

There are a couple threads, or posts within threads, where people have discussed the inner workings of the ECUs.
 
I don't know anything about Proform distributors, but here is an example

Many of us run GM HEI modules rather than the Mopar ECU. The GM module is quite different, and controls the coil current. I run my stock old Mopar coil with a GM HEI, and NO resistor at all, and it works fine. Also, the GM module does NOT draw coil current if you leave the key "on" with the engine stopped.

The Mopar ECU does not control coil current, which is why you can destroy coils or modules with that system.

That is just one example. What I'm getting at, is the Proform system may tolerate more (or less!!) current than the Mopar ECU can handle.

So what is the answer? Maybe try to find someone who can "cough up" just what a Proform can handle.
 
You must log in or register to reply here.
-

Back
Top