My coil was bad, so I bought a MSD Blaster 2, planning on doing the HEI conversion later. But, right now I just want to get the engine started (I have a new engine, not yet installed, will be installed in a couple of days).

So before I do the HEI conversion, I want to make sure everything works and I can start the engine. The Blaster came with a 0.8 ohm ballast resistor.

My question, should I use the ballast resistor that came with Blaster, or does it matter? It would make sense to me to use it, except the original ballst is a dual ballast and the new one is a single. What is the purpose of the dual, and is its function too important to change it to the single ballast that came with the Blaster?

What's the resistance of the msd coil? If it's lower than the stock coil, you may need to use the stock ballast (low resistance side) AND the MSD ballast so you don't burn out the existing module. You're probably better off just using the stock coil until you do the HEI.

The original ballast had 1 side for the coil and the other for the ignition module. The higher resistance side went to the ignition module and isn't needed with a HEI.

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

I wouldn't have even bought a new coil yet, but the stock coil had an oil leak. I figured since I needed a new coil, I would buy one that I could use for the conversion. The Blaster resistance specs are:

Primary Resistance: 0.700 ohms
Secondary Resistance: 4.70K ohms

I've measured the R vs I curve for a stock point-type ballast; it can be approximated as

R[ohm]=0.5+ 0.633 I[A].

The stock coil has a primary resistance of ~1.5ohm and is reported to have an inductance of ~2.4mH. The inductance of the MSD coil is said to be 8.0mH.

Larger inductance means more spark energy, but a longer RL time constant required to charge up for the next spark.

The stock point system would draw ~2.8A at idle and just replacing the stock coil with the MSD would draw ~2.5A. The larger inductance would provide 3.6-2.1x more energy over the range 600-5900rpm.
If you then replaced the point type ballast w/ a fixed 0.8 ohm you'd get ~6.3A; quite abit higher than stock and probably hard on points. If you put the two ballasts in series you'd get ~2.8A, but get a weaker spark than stock above ~2700rpm.

In summary, I'd just use the stock ballast for now if you're running points. If you're running a stock electronic system, it wouldn't matter much which you used.

Thanks. It is (so far) the stock electronic ignition (73 Dart Swinger, 68 engine)

I assume "which" means you should be using _something_.

Some have said you need no ballast at all with HEI if you use a certain kind of coil (one site merely says "aftermarker coil"). It's not clear to me exactly what's at stake here. Can you illucidate?

Thanks

I want to start my new engine with the stock ignition before I make the HEI conversion (make sure my current ignition system works before I start cutting wires for the conversion). But my stock coil was bad, so I replaced it the Blaster cause I didn't want to buy two coils.

You're right. I was off topic - thnking about the far end of that process.

The reason I want to start this with the stock ignition first is, the car has never run since I've owned it and have really no idea what works and what doesn't.

However, I finally got the electrical system working yesterday. I got the battery hooked up and the windshield wipers were going, the hazard lights were flashing, and with the door open and the key in, the most annoying buzzer in world was buzzing . Anyway, all the lights, blinkers, horn, wipers, cig lighter, volt gauge, worked .