Ballast resisters
Which edition (or cover)?
Looks like its probably earlier than the one I cited. Sorry to see it also has the same terrible copy editting. :(
Here is information that I found that talks about MP ECU's and MSDs.
This is true with a CD ignition like MSD, Mallory And Crane sell or with any ECU that is internally regulated(like GM HEI or Pertronics). According to MSD(this is not me making this stuff up) the Mopar boxes are not internally regulated and need to have a total resistance (coil primary + ballast) of at least 1.5 ohms. The Blaster2 coil has .7 ohms of primary resistance and comes with a .8 ohm resister for a total of 1.5 ohms. MP's literature on ballast resistors is confusing at best and many catalogs and advertisements incorrectly state that an Orange box and Blaster2 coil can use a .25 resistor. Maybe this is one reason the Orange box has such a bad reputation.
The .25 resister is for racing with a chrome box and a 100 wind coil equivalent to the blaster2. Use under 3000rpm should be limited to less than 30 minutes to avoid overheating the ecu. With no resister it would overheat even faster. Just like the orange box, for street use a .8ohm or more resister is necessary.
That all sounds familiar, and always seemed about right. However, this morning it seemed worth trying to verify the key assertion that 1.5 Ohms is needed.
1976 FSM under electrics shows two coils; one with with primary resistance of 1.6 to 1.79 ohms, the other 1.41 to 1.62 ohms (at 70-80*F).
Same service manual specs the ballast resistor coil side to be .5 to .6 ohms.
Added together equals 1.91 ohms minimum and 2.39 ohms maximum.
Well, that's over 1.5 ohms, and 'they' did say minimum. But I suspect the turns ratio also plays a role. ??? need to brush up on inductance and its effect on current if any, impedance anyone?
"ECU that is internally regulated"
The ballast resistor we're discussing is not used for ECU regulation, its for controlling current through the coil. However, HEI modules regulate coil current and that's probably what the author meant. Factory ECU's connected to a dual ballast resistor, did use the second resistor to reduce their internal operating voltage.
