Electronic Ignitions 101

Electronic Ignitions 101.
by Ray Sedman

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 following takes some liberties with application theory and is not meant to be a white paper on the matter. It is, more or less, electronic ignitions 101.

ELECTRONIC POINTS REPLACEMENTS.

Many times people refer to 'electronic ignition' and what they really mean is 'electronic points replacement'. These are typically the Ignitor, the Crane electronic points replacement [light trigger] and the Dale Manufacturing Chrysler conversion. These are the popular ones now and many other systems have graced the market over the years.

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.

CD and HO TRANSISTORIZED ELECTRONIC IGNITION SYSTEMS.

An electronic ignition system would be a electronic control of the ignition system, usually with additional features, like increased output, multiple spark, capacitive discharge, etc. MSD 6 and 7 systems, Crane HI-6, some Mallory systems, SafeGuard, Delta Mark 10, etc., are typical examples for electronic ignition systems.

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.

DWELL.

Dwell is measured in degrees and is the amount of 'time' the points stay closed. When the points are closed, the coil is building up charge (inductive). When the points open the coil releases it's charge.

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.

DWELL CONTROL.

Active dwell control is a very clever [electronic] way to further increase the output of the coil. With active dwell control the system is constantly monitoring the coil output and actively varying the dwell for maximum coil saturation. This does wonders for actual spark output. Another way to describe this would be 'constant on time dwell'.

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 this. Some of the newer OEM systems incorporate active dwell control, most aftermarket systems do not and as discussed above, CD systems can not use dwell control. The SafeGuard is one of the few aftermarket systems that has active dwell control.

TRIGGERING.

All electronic ignition systems need to be triggered by some 'device'. Depending on the system, triggering can be via points, electronic points conversions, inductive or Hall Effect magnetic trigger system. To most systems, electronic points conversion 'look' the same as the points. For example; the electronic points conversions output a signal/waveform which 'looks' like a point system. This is important to note, because most coils are designed to trigger from a 'points' source.

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.

SPARK OUTPUT vs. ENERGY REQUIRED.

Many systems claim higher output energy than a stock system, but can you use it? An ignition system will only output the energy required to 'jump' across the spark plug gap. This is true whether the system claims to output 50,000 volts or 18,000 volts. The highest demands on an ignition system is during low rpm, full throttle acceleration for non turbocharged engines and boost conditions for turbocharged engines. Having 30,000 volts 'extra' will not help you if you do not need it. This is why most systems recommend that you increase your spark plug gap over factory specifications. The HO systems have more output to 'jump' a larger gap whereas the stock system may not. If you install a HO system and keep your gap 'stock' you may not notice any benefit. Many other factors effect ignition requirements like mixture strength [lean requires more spark output] engine condition [oil burning requires more spark output] high compression [requires more spark output]. So you see, there are times where you can benefit from more ignition power.....but is more better?

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.

ANALOG vs. DIGITAL SYSTEMS.

Of the systems discussed, the only two systems that are fully digital controlled are the SafeGuard and the Crane HI-6. The other systems are analog controlled. Digital controlled systems may have advantages over analog systems - this really depends on just what you want the system to do. If all you are doing is firing a coil and nothing else, then an analog system will do just fine. In contrast if you want to digitally control a REV limiter or attempt individual cylinder knock control, then you would be hard pressed to do this with analog circuitry.

ADDED FEATURES.

Electronic systems can get pretty elaborate. Since the system is controlling the spark of your engine, they can start controlling other functions as well. The most common one is REV limit control, but you can get much more elaborate. For example, the SafeGuard is able to control your engine at the individual cylinder level. It's primary function is to control detonation, thus it is able to retard the timing to individual cylinders to prevent detonation.

PARTING NOTES.

So, before you decide to purchase an electronic ignition system for your Corvair, ask yourself some questions.

Do I really need it? What am I doing with the car and why do I think I need it? Do you want to increase performance, increase fuel economy, control detonation, etc? Maybe there are more cost effective ways to obtain your goals. Have you tried to correct the problem first? Visit your local Corvair repair shop or check the CORSA Tech Guide. Do not start throwing 'Band-Aids' at your car until you have done all your home work and brought it up to 'factory specs' first.
What benefits will the system offer me? Sometimes it is difficult to separate the marketing hype from the facts. One manufacturer of aftermarket systems [not mentioned in this document] is so blatant in printing false and misleading statements about their product it just upsets me to no end. So, as with everything else, ask around and do your research before you purchase.
Do I anticipate that I will need other features in the future, like: Knock Retard/Timing control, REV limiter, Air/Fuel display monitor, Retard/Timing display, etc. Will the system I am considering have these available? If so, how expensive are they? Add the cost of these 'extras' into the system price.
Is the system built specific for the Corvair? Does the system include Corvair specific installation instructions? (Sorry, I just could not help that shameless plug )

Cheers!

Ray

Links.

For more information on the above systems, see the following sites: