Modified Mustangs & Fords
Ignition System Basics
Power Begins With A Single, Simple, All-Important Spark
We're always looking for ways to make more power without spending too much money. We bolt on carburetors and intake manifolds. We also perform cam swaps in our quest for power. When that doesn't meet our expectations, we step up to better heads and a valvetrain that can handle the task. But how often do we take a good look at the ignition system for performance improvements? Truth is, we don't look at it often enough.
Our ignition systems don't always concern us because if we don't understand it, why bother with it? But that's just cruising along with our heads in the proverbial sand. Understanding is the key to learning how to make it better. Your Ford's ignition system is a case in point. If you're running around with a point-triggered ignition system, you really are in the dark ages. There's better stuff out there, but it goes way beyond that. You need to know how your Ford's ignition system works, and how to tune it for better performance. So, belly up to the workbench, and let's get started.
The power that comes from a healthy mixture light-off cannot be underestimated. All it takes is a modest spark to ignite the air/fuel mixture under compression. However, the more potent the spark, the more aggressive the light-off. We not only need a spark, we need a potent spark timed just right in the combustion cycle to get things started. It's easy to ignite a fuel/air mix with the engine at idle power. it becomes complicated when our engine begins to rev higher, and spark timing and intensity need to change with the increase in rpm.
In The Old Days
In the early days of internal combustion engines, the basic principles of four-stroke operation wasn't much different than they are today: intake, compression/ignition, power, and exhaust. There had to be a means of storing high-energy electricity until it was needed to fire spark plugs. That system consisted of breaker points, a condenser, and an ignition coil to store the current. Point timing had to tie in with spark timing via the distributor rotor indexing. Spark timing had to follow a timing pattern with engine rpm. Then, as now, the spark needed to occur earlier and earlier in the compression stroke as the engine revved higher. In the beginning, the driver controlled spark timing from the driver seat. As engine revs increased, the driver advanced the spark timing. As rpm dropped, spark timing was retarded. It was crude, but it worked.
In time, automotive engineers developed spark-advance mechanisms that advanced the spark automatically as engine rpm increased. It was a simple flyweight system that advanced the spark as engine revs (and distributor speed) increased. The vacuum advance came along later to compliment the mechanical advance. The combination of the two types of advance units offered motorists a seamless transition from idle to power mode. Leaning on the throttle worked the vacuum advance (breaker plate) to get the vehicle moving. The mechanical (centrifugal) advance advanced the rotor indexing at higher revs.Think of it this way--the vacuum advance advances the breaker plate positioning when we're under initial acceleration. As vehicle speed and engine revs roll into higher rpm ranges, the centrifugal flyweights swing outward and advance the rotor positioning for an earlier spark.
We want an earlier spark at high revs because fuel doesn't ignite the way we think it does inside an engine. When we think of the four-stroke cycle, we think intake, compression/ignition, power, exhaust, but it's more complicated than that. Fuel and air do not "explode" in the combustion chamber like we were taught in Auto Shop 101. Fuel ignites in a quick-fire like it does in your water heater or furnace with a woof. If you've ever been startled by a sudden furnace or water heater light-up when you were lighting the pilot light and felt the blast of heat and air, you experienced the energy of thermal expansion. This is the same kind of energy that powers your engine.
As the piston rises in the cylinder on compression/ignition stroke, the fuel does not ignite at top-dead-center (TDC). The fuel needs to be ignited around 6 to 12 degrees before top-dead-center (BTDC) because fuel does not ignite instantly. It lights more slowly than we think. We have to allow the piston time to reach TDC before full combustion is underway. When we increase rpm, we need to allow the richer fuel charge more time to ignite. This is why we "advance" the spark and make it occur earlier during the compression/ignition stroke. Most of the time, that is 34-36 degrees BTDC. Pushing the spark timing any earlier can cause detonation and engine damage.
We can explain current saturation and how the ignition coil stores electricity, but that's not going to mean much to most of you. You want to know what the ignition coil's basic job is, and how it releases that high-voltage spark in time with the engine's power cycles. The ignition coil does its job in time with the ignition points located inside the distributor. Ignition points are nothing more than a simple on/off switch that allows the ignition coil (a transformer) to store and discharge thousands of volts of direct current electricity supplied by your Ford's 6- or 12-volt storage battery. As a simple high-output transformer, the coil transforms 12 volts to as much as 50,000 volts in order to jump the spark-plug gap. The points cycle open (off) and close (on) between spark-plug firings in time with the distributor cam. When the points are closed, the coil is grounded via the contact points. When the points are open, the coil grounds through the spark-plug wire to the spark plug.
Point-triggered ignition systems served a valuable purpose for decades and, all things considered, did remarkably well. However, points suffer from distinct disadvantages, as well. With use, contact points burn and pit. The rubbing blocks wear out, which causes the points to close up. This makes your engine a dead player when you probably need it most. Ignition points don't offer the reliability we get from solid-state ignition systems.
Solid-state ignition systems, as their name implies, are solid state--no moving parts to wear out. Magnetic pulse ignitions have a pick-up coil and a reluctor. As the reluctor passes across the magnetic coil, it switches the coil's ground path on and off, just like contact points do. This is also performed with the help of solid-state circuitry in an ignition module.
There are also optical electronic-ignition systems that use a light beam (electric eye) to open and close the coil's grounding path using a shutter wheel. Mallory's Unilite ignition is one example still available today. The only maintenance required is the occasional cleaning of the light module.
The Pertronix Ignitor and Ignitor II are undoubtedly the greatest innovation in aftermarket electronic-ignition systems because they're hidden inside your factory or aftermarket distributor. The Ignitor and Ignitor II are compact modules that replace the points and condenser in point-triggered distributors. These little guys are triggered the same way a magnetic pulse ignition is triggered. Set the air gap between the module and the shutter wheel and forget it. The Ignitor and Ignitor II are not only available for factory distributors, but selected aftermarket distributors, as well. This gives your restomod a cool, period, aftermarket, performance look with the fierce reliability of the Pertronix Ignitor.
Not only do we need good ignition systems, we need components that enhance our ignition system's performance. There are all kinds of spark enhancers that keep the plugs firing under extreme circumstances. High-output ignition coils, multi-spark discharge, capacitive discharge, and other types of high-output systems are available. Let's look at some from MSD.
You've Got The Power
This area gets as much respect as the rear axle. It is something we never think about until there's no choice. High-energy ignition systems need high energy to begin with. If you think that old generator or 45-amp Autolite alternator is going to get you through the night, you're only whistling in the dark. Truth is, you will be sitting in the dark.
For an electronic-ignition system to work effectively, you must have a high-output alternator. Ideally, you will ditch the voltage regulator and opt for a single-wire, no-brainer alternator that makes 100-plus amps of charging system power. This not only benefits your ignition system, but all those electronic do-dads you plan to install inside the cabin.