I am posting this as a possible reference for those wanting to use the readily accessible MSD Blaster II ignition coil with the DuraSpark II ICM.
The 1.82 Ohm ballast resistor show below will produce a 2.52 Ohm combined resistance when used with the MSD Blaster II (.70 Ohm), which should safely load the DuraSpark II ICM while maximizing the coils potential output.
http://www.jegs.com/i/Moroso/710/72390/10002/-1 (http://www.jegs.com/i/Moroso/710/72390/10002/-1)
With that setup the resistor will create a 8.66 voltage drop, delivering only 3.33 volts to the coil. That means the coil will only be able to put out 27.7% of its potential voltage. So that means the most voltage delivered to the spark plugs would be 12500 volts. That's less than the stock setup.
Much better off getting the pertronix 3.0 ohm coil and bypassing the resistor wire, this way the coil gets 12 volts allowing it to put out 40000 volts while not drawing to much current on the ignition module.
Quote from: ammachine390 on September 08, 2012, 03:59:28 AM
With that setup the resistor will create a 8.66 voltage drop, delivering only 3.33 volts to the coil. That means the coil will only be able to put out 27.7% of its potential voltage. So that means the most voltage delivered to the spark plugs would be 12500 volts. That's less than the stock setup.
Much better off getting the pertronix 3.0 ohm coil and bypassing the resistor wire, this way the coil gets 12 volts allowing it to put out 40000 volts while not drawing to much current on the ignition module.
Yes, ofcourse you are correct assuming the system in question delivered 12 Volts (not counting coil resistance). Our Eagles deliver over 14 Volts continuously!
Infact, the lowest continuous output that I have measure from a properly working ignition system is 13.8 Volts (Mercedes). 12 is wishful thinking without a resistor (again, not counting coil resistance).
However, you are right in the long run because even at 14 Volts, it still doesn't deliver (and I should have done a better job of calculating it!).
The biggest problem I have found is running a coil with 14+ Volts continuously. I am not personally aware of a single street coil that can handle it for long, are you?
Is this not the true reason for the reported Pertronix failures?
Quote from: Mernsy on September 08, 2012, 05:26:58 AM
I've been running the Petronix coil at system voltage for four or five years, including one thousand mile trip. Never heard of them failing 'til now. Guess I better keep a spare on hand.
I did the "big cap" (TFI) upgrade and used the Pertronix 3.0 ohm coil. The coil lasted less than 1,000 miles. I replaced it with the E Core coil that came with the kit from GRONK.
I don't think that it's specific to the Pertronix, I've heard of other coils failing out of the box. Just because one is bad, doesn't mean they all are. I've had mine now for over 1 year, and never a problem. I believe Jurjen has had his now for 4-5 years and no problems as well.
Quote from: rollguy on September 08, 2012, 11:05:03 AM
I did the "big cap" (TFI) upgrade and used the Pertronix 3.0 ohm coil. The coil lasted less than 1,000 miles. I replaced it with the E Core coil that came with the kit from GRONK.
My own collective experience has shown the majority of E-coils fail within 2 years if not kept in the 12 Volt range! whether its a built-in limitation, or a problem with the quality of parts made available to us I cannot say.
In any case, I am going to stick to my plan of using an external HEI coil and module + TFI upgraded Motorcraft distributor.
I just need to find a bad DuraSpark ICM to mount the module in.
There is also the ACCEL 140207, which is basically a high voltage version of the stock coil. But according to another poster, the coil is only good for 22,500 Volts using the required stock resistor value (1.35 Ohms).
While it is good enough for me, the question comes down to the optimal spark plug gap.
Quote from: George Mann on September 08, 2012, 06:23:48 PM
There is also the ACCEL 140207, which is basically a high voltage version of the stock coil. But according to another poster, the coil is only good for 22,500 Volts using the required stock resistor value (1.35 Ohms).
While it is good enough for me, the question comes down to the optimal spark plug gap.
Careful about using the 140207 Accel Coil. The stock horsehoe connector doesnt fit it too well. (Poor design if you ask me..I tried my orginal connector, one I snagged from a 81 Ford Truck and a brand new connector from Napa, none fit right). And if you dont get it jammed on there enough, lots of missing..