Point-triggered (breaker-point) ignition is a simple on/off switch that opens and closes the primary ignition circuit to charge the coil and reduce a brief discharge of high-energy current to fire a spark plug. It can be debated who invented the breaker high-energy discharge ignition system, but who cares? What you’re interested in knowing is how it works and how to make it better.
When you turn on the ignition switch, power travels to the primary ignition circuit to energize the coil and breaker points. Current travels through resistance wire in a Ford to the primary circuit. If points are closed, current fl ow across the contact points tends to burn the contacts. As current flows through the primary side of the ignition coil, it creates a strong magnetic field, which in turn induces a huge surge of current on the secondary side to the distributor. The condenser is there to take up the surge of high-energy electricity, which would otherwise arc violently across the open point gap. This action would quickly burn and pit the contacts. The condenser also allows the ignition system to build an electrical momentum to a steady 20,000 to 30,000 volts to the secondary side to fire the spark plugs.
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The average garage mechanic tells you an engine can run without the condenser. However, engines generally don’t run very well without condensers because the condenser acts as an electrical cushion— a shock absorber for high-energy electricity. Without it, electricity returns to ground, arcing across the points, and being of little value to operation.
Dwell Time
Ignition points are a rotary camactuated switch that operates in time with your Cleveland’s firing order. This switch turns electricity on and off through the ignition coil. Dwell time is the amount of time in distributor shaft rotation degrees that points are closed. Each time the points open, a spark plug fires. With a dual-point distributor, dwell time is increased to build more coil saturation and get a more potent spark. You also eliminate the limitations of a single set of ignition points, which are point bounce and incomplete coil collapse especially at high RPM. Key to improved performance is increased dwell time and a stronger spark. When you widen the point gap, you increase dwell time.
Electronic Ignition
The main reason automakers went to electronic ignition in the 1970s wasn’t so much for performance, but reducing emissions because every misfire is unburned hydrocarbons and increased emissions. If you listen to new cars and trucks today, they don’t misfire. That comes from a potent high-energy spark and the precision of electronic fuel injection.
Ford’s Duraspark II electronic ignition offers the greatest reliability of any electronic ignition system. It is good well into high RPM and enjoys widespread parts availability. Aside from rotor and cap replacement once in a great while, Duraspark II is maintenance-free. You can mount the ignition amplify er anywhere using a Painless Performance Duraspark wiring harness.
Despite a point-triggered ignition’s time-proven ability to fire spark plugs with precision accuracy, it has shortcomings. As you increase engine speed, there’s less dwell time to build adequate current, which reduces spark potency. This causes misfire at high RPM because you need a spark powerful enough to overcome high cylinder pressures. At high RPM, points tend to bounce and fl utter, also causing misfire. These shortcomings prompted creation of other types of ignition systems, such as transistorized ignition, triggered electronic ignition (Hall Effect), and capacitive-discharge ignition.
Transistorized Ignition
Ford was among the first to use transistorized ignition in the early 1960s. And later, Duraspark in 1975. Chrysler was the first US automaker to go with electronic ignition in 1974. Somewhere in there was General Motors’ first shot at magnetic-triggered electronic ignition, then HEI (high energy ignition) in the late 1970s. HEI was a great idea because it eliminated the external ignition coil.
Triggered Electronic Ignition System
There have also been light-triggered electronic ignition systems with shutterwheel triggers and light-emitting diodes (LEDs), such as Mallory’s Unilite ignition in the 1970s. Light-triggered ignitions have performed very well and with great reliability. Most electronic ignition systems since the 1970s have been Hall Effect (magnetic-trigger) systems, which are the most reliable. In fact, even in this age of coil-on-plug, fuel injected engine control systems, Hall Effect is still used in the crank trigger role.
Capacitive-Discharge Ignition
Combining electronic ignition with capacitive discharge allows an inductive type of ignition system to build tremendous amounts of electricity for the secondary side to fire spark plugs. These systems pack a wallop and discharge huge amounts of electricity for each spark plug firing. In fact, these systems are designed to handle up to 12,000 rpm, which most Clevelands never see.
Pertronix Ignitor series electronic ignition retrofit kits are the 30-minute solution to all of the problems associated with pointtriggered ignition systems. Simply remove your points and condenser, bypass the factory resistor wire (which unplugs near the ignition switch), and install the Ignitor. Set the air gap, make sure you have the ground link, and you’re good to go.
This is a ballast resistor, which is common with Chrysler ignitions, but can be used with any ignition system requiring resistance in the power lead. When you purchase and install an aftermarket ignition, read the manufacturer’s instructions carefully. Some require a resistor and some do not. Be sure to use the exact resistance required by the +manufacturer.
Remember, if you’re going with a roller cam of any kind, replace your distributor’s iron drive gear with a steel gear. Brass drive gears work well, but they don’t last. (Comp Cams offers a composite distributor drive gear that wears quite well.) Keep in mind there are two distributor shaft sizes: .530 and .467 inch.
It’s important to have distributor shaft end play within Ford specs to eliminate any chance of extreme wear. You can make your own “go/no-go” gauge (such as this one created by Marvin McAfee of MCE Engines) to make the job of checking easier. Shaft end play should be .024 to .035 inch. Be sure to measure distributor drive gear to block gap. Gap shown here is .012 inch. This allows room for end play, thermal expansion, and oil wedge.
Ignition wires should be spaced apart to prevent crossfire. Crossfire happens more often than you think, including with new ignition wires and with a high-energy ignition system. Crossfire can do serious engine damage especially if it happens at high RPM.
When installing ignition wires, use a dielectric compound and make sure terminals are seated completely in the distributor cap and on spark plugs. Arcing damages terminals and only makes the situation worse.
Street engines get a vacuum advance; racing applications do not. For street and strip, go with a vacuum-advance ignition for better fuel economy and low-end torque.
A simple failsafe modification to keep the distributor cap secure at high RPM is to use a zip tie. Although this might be viewed as overkill, it sure beats losing the cap at seven grand.
The key to performance and cleaner emissions is a potent spark. How you get that potent spark depends on your support system and what you use for spark enhancement. MSD Ignition, as one example, has a variety of ignition enhancement systems—most of which are based on capacitive discharge. The MSD 6A ignition enhancers are based on this principle, and they do an outstanding job of keeping the fire lit at high RPM. One MSD enhancer, the 6 BTM (Boost Timing Master) allows you to control spark timing if you’re running a supercharger or nitrous, which helps keep you out of trouble when things get hot and your foot is in it.
Ignition Coils
Most factory Ford ignition coils from the early 1970s make approximately 20,000 to 30,000 volts. This makes them inadequate for high-performance use. Stock ignition coils work fine for normal driving at low- to mid-range RPM. However, when you start spinning a Cleveland beyond 6,000 rpm at wide-open throttle, a factory coil cannot keep up. It continues to fire spark plugs, but not at the intensity they need to light the mixture. This is a combination of dwell/saturation time and spark potency.
At high RPM under great cylinder pressures, a weak spark gets snuffed out, hindering its ability to light the mixture. If you add supercharging or nitrous, it quickly becomes overwhelming. This is why you want a powerful ignition coil coupled with an ignition enhancer such as a capacitive or multi-spark discharge. You want the most spark your ignition system can pack, even with a street engine.
Written by George Reid and Republished with Permission of CarTech Inc
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