Ray Sedman wrote this article for Virtual Vairs on electronic ignitions, including pros and cons of various systems. I have included some links to the manufacturer's sites at the bottom of the page.
There have been some very good posts on electronic ignitions in the past few weeks, so I will not re-hash that stuff. Brian Dierks, Rad Davis and many others have posted some very well written documents on this subject. If you do not have these posts, check the VV archives because they contain information which dovetails with the following.
The purpose of this post is to fill in some details of the recent posts
regarding 'electronic ignitions', package everything in one 'little' post
and, at the same time, give me the opportunity to shamelessly 'plug' the
SafeGuard individual cylinder knock retard system.
The design of these systems is to replace the points and use a electronic trigger to fire the coil. The electronic trigger can be a photo diode (Crane) or an inductive or Hall Effect magnetic trigger system (Ignitor & Dale). These systems will typically increase energy available to the spark plugs because of the more efficient triggering system and they are less prone to problems associated with points trigger. Some of the problems associated with points trigger are: rubbing block friction/wear causing 'shrinking' point gap, point bounce, distributor shaft play causing inaccurate spark timing or misfire and points contact erosion since the points are a 'high current' switch. So replacing the points with an electronic points replacement system generally give a positive performance to most engines.
Of the electronic ignition systems these can be divided into two major categories. Capacitive Discharge (CD) and High Output Transistorized (HO). As discussed on Virtual Vairs, Capacitive Discharge basically works by charging a large capacitor, which stores energy, and 'flashing' the coil with a very high output (volts). This typically is in the range of 450 volts. The MSD, Delta Mark Ten and Crane HI-6 systems are typical CD systems. High Output (HO) transistorized systems use a power amplifier circuit to drive the coil with more power (amps). This is done by using the coil as an inductive storage device hereby increasing the coil output. Some Mallory systems and the SafeGuard are HO systems. For reference, an G.M. HEI system is another example of a HO system. Once you have an electronic ignition system you can then start adding some 'fancy' control electronics to help matters further.
When using a CD system, dwell becomes meaningless. This is because the CD system stores the energy [in a capacitor] and sends it to the coil when it is needed [points open]. The output of the CD system is very fast and very 'hot', thus the coil does not 'saturate' with dwell time, it just, for lack of a better phrase, "shoots it's wad" in one short, hot, burst. In contrast, HO systems store the energy in the coil by inductive means. The HO system inductively stores the energy in the coil's windings until time to pass it to the distributor cap. CD systems store energy in on-board capacitors whereas the HO systems 'stores' the energy in the coil during dwell time. Because of this, one can do some pretty fancy things with non CD, HO systems and use the dwell time to a great advantage.
It is amazing to watch this in action - attach a dwell meter to an engine with active dwell control and watch it work.
At idle the dwell will be 10-15 degrees. As you bring the RPMs up the dwell
will increase - all the way up to 50 degrees or so. The dwell increase is
rock steady and proportional to RPM. I have had some fun with a few
'technicians' asking them to try and find out why my engine is acting like
Looking at the Dale Chrysler conversion and the Crane 'light' trigger we find an external control box. The purpose of the box is to convert the electronic signal generated by the 'points replacement electronics' and output a signal/waveform that can fire the coil. The Ignitor looks different because it does not have an external box, but all the necessary 'electronics' are enclosed internally in the Ignitor. So, all these systems will output a signal/waveform that 'looks' like points to fire a coil. Think of these systems as 'two systems in one'. The first system is the trigger system and the second system does the conversion of the 'trigger' waveform to make it look like 'points' to the coil.
Some systems, MSD, Crane HI-6 and SafeGuard can be triggered directly from a inductive or Hall Effect magnetic trigger system as well as a 'points' system. To do this these systems must include additional electronics to do the conversion of the input signal (inductive) and output a 'points' signal to fire the coil. Why, how, would this be helpful? Good question. This would be helpful if you wanted to run your Dale Chrysler conversion without the external control box, directly to a SafeGuard individual cylinder knock retard system. The same holds true for the MSD and Crane HI-6 systems. You could use your Crane 'light' trigger without the external control box to drive your Crane HI-6 CD system or your MSD.
There is a practical limit to the amount of energy you can 'contain' in the small Corvair distributor cap before you start having problems with cross firing, arcing or burning. Look at any newer car and you will notice the distributor cap is much larger in diameter. There is a good reason for this.
As you increase the energy available to fire the spark plugs you reduce the chance that the output will actually go to the spark plug and not find a 'better' ground. Electricity will find the 'shortest' path to ground and if the energy required to jump [cross fire] inside your distributor cap is less than required to jump across your spark plug gap, it will do so. This can be a problem. It is common to install a quality CD or HO ignition system on your Corvair and then start having ignition problems that you never had before. First to be 'blamed' is the last part that you put on. In this case it is the electronic ignition system which is falsely blamed.
Anytime you update/increase your ignition system's output you should also pay special note to your other ignition components. For example, your old spark plug wires that gave you no problems before may vary likely be 'leaking' voltage now with the increased power. Your distributor cap, worked just fine, but now shows signs of pitted contacts and burned rotor. Time to call or visit your favorite Corvair vendor and get some new, quality parts.
The preferred parts would be a cap and rotor with brass contacts [typical caps have aluminum contacts] and a premium plug wire set. Get your parts and especially the plug wires from a Corvair vendor. They will have correct spark plug boots [very important] that are known to fit perfectly and are of fine quality. Most 'universal' type wire sets will not have the required boots and you will pay more for 'less' product. Don't forget fresh, correct, spark plugs also.
The small Corvair distributor cap makes good ignition 'house keeping' mandatory with any HO or CD system. You must keep all connections clean, oil free and in good order. If you have a small defect, you will be the first to know when you install your new, higher output system.