Ignition System Basics

Power Begins With A Single, Simple, All-Important Spark

By Jim Smart

Photography by Jim Smart

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.