Unilite, MBI and E-Spark: The Real Deal (long)

Discussion in 'Classic Mustang Specific Tech' started by RobbMc, Dec 5, 2003.

  1. I hear so many myths and partial truths about Mallory ignition modules that I thought I'd try posting the facts on a the forum to clear things up.

    Mallory has three types of modules (not including the new rev limiting HEI module) that fit inside the distributor: Unilite, Magnetic Breakerless Ignition (MBI) and the new E-Spark. The Unilite and E-Spark are similar but the E-Spark is manufactured on automated equipment to reduce manufacturing costs so that the E-Spark conversion kits can be sold at about the same price as a Pertronix. The MBI uses a similar circuit but uses a magnetic pickup as a triggering device rather than an optical pickup.

    The Unilite and the MBI are available in complete Mallory distributors. The Unilite and the E-Spark are available in conversion kits for stock type point distributors.

    All three modules were originally designed to replace point style ignitions. Point style ignitions use coils with high primary resistance and ballast resistors (or resistor wires such as used in AMC, Ford and GM). Thus, the Mallory modules were designed to use a ballast or resistor wire.

    Unilite, MBI and E-Spark modules (and Pertronix) are basicly electronic replacements for points. They are not amplifier boxes like a Hyfire or an MSD box. They are simply a way to get rid of the points. The spark output is usually a little higher than points due to the increased dwell time (and you don't have to worry about point bounce) but the output is not significantly greater than points. HEI type modules or external amplifier boxes are the only way to significantly increase spark output.

    All three Mallory modules wire the same way. There are three wires:

    The brown wire is grounded to the engine. Make sure you also have a good ground cable/strap between the engine and the frame/battery. Do NOT ground the brown wire from the module directly to the frame or battery. If you do, the brown wire will become a ground for the starter during cranking which will melt the brown wire and take out the module.

    The green wire connects to the negative side of the coil.

    The red wire can connect to the positive side of the coil but it's better to connect it to the high side (12 volt) of the ballast resistor. Remember, the ballast or resistor wire is there to limit the current through the coil and the green wire. The red wire prefers to see full battery voltage. If you connect the red wire to the positive side of the coil (which is also the low side of the ballast) the engine may not start as easy especially if the battery is low. If your car has a resistor wire rather than a ballast, you can either hook the red wire to the positive side of the coil, or better yet, find a place to hook it that will feed the red wire full battery voltage whenever the key is on.

    If you are also using an external box such as a Hyfire or MSD, follow the wiring instructions that come with the box as the module will need to be wired differently. A ballast or resistor wire is not needed when using an external box since all the current for the coil goes through the box rather than the module. (When used with an external box, modules and points last almost forever because very little current goes through them). Some people like to leave the ballast or resistor wire in place when hooking up an external box (it won't hurt anything) so that if the box fails you can bypass the box and still get home running on the module alone.

    I often hear people ask what voltage they should have at the coil when running a Mallory module without an external box. The standard answer is about 7 to 10 volts measured at the coil with the engine running. However, while this is easy to measure, it is not the best thing to measure since the voltage will vary depending on the voltage output of the alternator. What really matters is the total resistance of the primary side of the ignition. This includes the ballast (or resistor wire) and the primary resistance in the coil (measured with an ohm meter between the positive and negative terminals on the coil). The ideal total resistance is a minimum of 1.4 ohms and a maximum of about 3.5 ohms. More than 3.5 ohms is safe for the module but the spark may be too weak for optimum performance. Use an ohm meter to measure the resistance across the ballast and add that to the amount of primary resistance in the coil. The total should be between 1.4 and 3.5 ohms. You may need to measure the resistance of the ballast after it has warmed up since some ballast resistors increase in resistance with temperature. If your car has a resistor wire rather than a ballast it can be difficult to measure the resistance in the wire as the wire gets lost in the harness. If so, assume that the resistance in the wire is about 1.0 ohms which is typical.

    Some coils have so much primary resistance that a ballast resistor or resistor wire is not necessary. Mallory has two new Promaster coils that have all the resistance built into the coil (29450 and 30450). Using these coils, no additional resistance is needed.

    Having all the resitance built into the coil has drawbacks however. The coil will run hotter which will reduce the life of the coil somewhat. Also, high resistance coils are not recommended for use with external boxes as the coils will overheat and fail (sometimes even explode!).

    Don't use solid core plug wires with any electronic igntion.

    If you weld on the car, disconnect the module before doing so.

    Unlike popular opinion, the standard Pertronix module also requires a certain minimum resistance. When using a Pertronix on a car that was using points, no ADDITIONAL resistor is needed, but this is also true for Mallory modules. Pertronix also sells their own coils with high resistance so that a ballast is not needed.

    Now you know the real deal.
  2. Can I use an E-spark module in my unilite distributor? I assume they're cheaper, and it would be nice to carry a spare.
  3. Yes, the E-Spark module can be used anywhere a Unilite module is used. Direct replacement.

    The E-Spark is being released this week at the PRI show. You should be able to buy them after Christmas. The price will be less than a Unilite module.
  4. What's the difference in performance between the two?
  5. Output is the same. Same dwell, same energy. The E-Spark is basically a modern version of the Unilite. Modern manufacturing lowers the cost. Modern circuit board design improves module life.
  6. when i bought my Stang it had been switched over to electronic (not sure what brand) along with an MSD coil. THe car had alot of backfiring problems and starting problems. I got so fed up that I put a rebuilt points distributor back and she runs good now. I prefer to stick with original equipment on my car. I think whomever had made that switchover didnt do something correctly. Just my two cents.
  7. Maybe I'm a bit behind, but I distinctly remember the instructions for the unilite saying NOT to connect the red directly to 12V, because it will cause the module to burn out prematurely. It's supposed to get between 6-9 V, which is about what the mustang has at the coil through the stock resistance wire.

    And some andecotal experience; If your battery is weak and won't spin the engine, and the distributor happens to be at a trigger point with the key in the start position, it'll fry the ground wire if held too long.
  8. No, as I said above, it is the wire that feeds the coil (ie the stock resistance wire) that needs the resistance. This prevents too much amperage through the coil and the GREEN wire to the module. The red wire works better when it gets full battery voltage. Many of the Mallory instructions say to connect the red wire to the positive side of the coil simply because this is easier and it will usually work. But if your battery is low or you live where it is very cold, your engine has a better chance of starting if the red wire sees full battery voltage. A resistor wire or a ballast IS needed, but NOT for the red wire.
    I am an engineer at Mallory and I am trying to rid the world of these myths.