Breaker point ignitions are simple and inexpensive. Unfortunately their power output is limited and they require routine maintenance to work properly. Breakerless electronic ignitions can put out more power than points but cost more money. The biggest selling point for breakerless electronic ignitions is low maintenance, you just set it and forget it... until it breaks. My dad had the ignition module on his '86 Mustang blow out twice in the four years he owned it. Points will wear down slowly retarding the timing, you will feel a loss in power well before it dies. Electronic ignitions don't give any warning. One minute you're driving, the next minute you're a pedestrian. Points can only handle about 4 amps. An electronic ignition must be able to handle at least 4 amps in a stock application and more on built motors with a racing coil. If you have ever seen the size of transistor and heat sink needed to RELIABLY handle 4+ amps then you will wonder how some electronic ignitions work. Most aftermarket and OE electronic ignition systems use small transistors to save money and increase profits. If you want a reliable electronic ignition then stay away from the little magic boxes that fit inside the distributor. There is a dirt cheap and reliable electronic ignition module that you can run on any motor and buy anywhere.
In 1973 Chrysler made their electronic ignition standard equipment. Mopar guys have know the benefits of this system since it came out. If your car is Mopar powered you can still buy a conversion kit. Most people don't know the Mopar ignition box can be hooked to any distributor, including points. You're probably thinking that running an electronic ignition off of points defeats the whole purpose. If you're putting on an electronic ignition because you want one less thing to maintain then you should spend more money and buy a magnetic pickup distributor. If you want the power of an electronic ignition but don't want to buy a new distributor then hook it to the points. The points simply act as a trigger, the ignition module determines the dwell and handles all the current (which are the two biggest limitations of points). Since the transistor in the box handles all the current you will never burn the points, no matter how many amps the coil is pulling. There is one advantage points have over a magnetic pickup. If the ignition module craps out in the middle of nowhere you can just bypass it and keep going. I was curious how well a Mopar box would work on my Ford 289 with points so I tried it out.
The first step was buying a box. I called every parts store and junk yard in town to find the best price. Only one junk yard had them and they wanted $15 for the box and wires. Every parts store I called had Mopar style ignition boxes. Prices ranged from $14.89 - $48.99. You can also buy high performance boxes made by Mopar. They recommend the orange box for up to 6,000 rpm, the chrome box for over 6,000 rpm, and the gold box for all out racing. I decided to go with the $21.99 box from NAPA, (it's made by Standard Motor Products) model #TP50SB. As you can see in the picture it uses a huge transistor and heat sink. I looked up the specs on the transistor, it can handle a continuous 15 amps and a peak 30 amps. That's way more than any set of points can handle.
To wire it up you could cut the wires out of a junk yard car or buy a wiring kit from Mopar for about $20. I just wired it up with what I had laying around. Small female bullet connectors fit the pins on the box perfectly. First you should mount the box. It needs a good ground connection to work properly so scrape any paint under it and make sure the screws are tight. The cooler it is the longer it will last so keep it away from headers and other heat sources. Normally the box is wired up using a magnetic pickup, see pic. Pin 1 hooks between the ignition switch and ballast resistor, pin 2 goes to the negative coil lead, and the pickup is wired to pins 4 and 5. If you're wiring it up to points you only need three wires. Pins 1 and 2 are the same, and pin 5 is wired to the breaker points, see pic. You can remove the condenser if you want, I tried it both with and without the condenser and it made no difference. You need to change the point gap. A standard breaker point ignition fires when the points open, the electronic ignition will fire when the points close. If you don't regap the points the ignition will fire when the rotor is between posts on the distributor cap. Most likely you will have to make the point gap as small as possible. The smaller gap allows you to lower the breaker spring tension which will prolong point life. To check rotor alignment just cut a hole next to one of the posts on an old distributor cap so you can see the rotor. Hook a timing light to the plug wire closest to the hole. With the motor running, watch the rotor with the timing light. Rev the motor while watching it because the rotor position will change as the vacuum advance comes in. Ideally you want the rotor directly under the post when the ignition fires. Mine was pretty close after adjusting the points, but I wanted it right on so I repositioned the distributor cap. All I did was widened the alignment slot on the distributor cap so I could turn it a few degrees.
It only took me a couple hours to hook up the box. When I fired it up I was amazed to see 43° dwell at idle (750 rpm). I didn't think a motor would run with that much dwell. The dwell goes down as the rpm increases. At 5500 rpm it is 35°. If you do the math you will see that all it is doing is turning off the coil for about one millisecond because the spark only last about a millisecond. That is a poor dwell control. Ideally you want to keep the coil charge time constant which would show up as only a few derees dwell at idle and would get higher as rpm increases. A coil holds a finite charge, once the maximum charge is reached any additional current is just turned to heat.
Using a ballast resistor to control current increases primary resistance which slows the coil charge. At high rpm there is not enough time to completely charge the coil. If you need more spark at a higher rpm then you can reduce, or eliminate, the ballast resistor or get a coil with a lower primary resistance. This builds heat at lower rpm and can burn out your coil. A cheap solution is to hook a relay to bypass the ballast resistor when you stab the gas. Wire the relay to a switch on the throttle or if you have nitrous you can wire the bypass relay to the same switch as the nitrous relays. This gives you extra spark when you need it and keeps the coil cool when you're cruising.
This electronic ignition cost me less than $25 and runs as good as my $75 dual point distributor. Besides being cheaper, the only real advantage to the Chrysler box over points is lower maintenance. If you're looking for more performance then spend a little more for a TFI.
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