At 7,000 rpm, a spark plug ignites the air/fuel mixture nearly 60 times per second. Any one of those 60 sparks going amiss can at best be mildly annoying, and at worst cost you a race or an engine. Now multiply that by eight cylinders, and it's easy to see why a properly functioning ignition system is paramount to performance and reliability.
Strangely, ignition systems are one of those things that hot rodders seldom think about until something goes wrong. Don't be one of those guys. To get schooled on how to set up a top-notch ignition system for your ride, and get the inside scoop behind the technology that makes it all possible, we had a long, electrifying chat with Don Lindfors of PerTronix Performance Products. Although the company's broad portfolio also includes exhaust companies like Doug's Headers and JBA Headers, we decided to focus on the PerTronix ignition line this go-round to keep things more manageable.
Originally known as Per-Lux, PerTronix was founded in 1962 with the bulk of its manufacturing focus on driving lights and fog lights for the big rig truck market. In the early 1970s, a Per-Lux engineer came up with the idea for an electronic ignition system that replaced the points and condenser in distributors. After patenting the product, PerLux started manufacturing the Ignitor, which originally catered to the fork lift and industrial engine markets. The product gained wide acceptance with fleet managers, who came to realize the dramatic improvement in reliability and reduced maintenance cost it offered. Only a few automotive applications were available in those early years, but automotive enthusiasts began using the Ignitor for the superior performance it offered. Utilizing the Ignitor technology, a complete electronic distributor was developed in 1985 and supplied to Wis-Con, an original equipment engine manufacturer. In 1991, through a series of corporation acquisitions and restructuring, the Per-Lux Ignition division was renamed PerTronix, signaling the company's total commitment to the ignition business.
Ignitions in Action
Most people are familiar with the components in an ignition system, such as the distributor, coil, plug wires, plugs, and ignition box. On the other hand, people are far less familiar with how all these parts work together to transfer the electrical charge from the battery into the combustion chambers. "It all starts with the voltage in the battery, which supplies power to the ignition system. When the driver turns the key, voltage is sent to the ignition coils, and as soon as the motor starts to turn over, the points or electronic module in the distributor opens and closes the circuit," Don explains "When they are closed, a current path of around 10 amps is flowing through the primary windings of the coil, creating a magnetic field within it. When the circuit opens, this primary current suddenly stops and the magnetic field collapses. This change in the magnetic field causes a sharp spike in the primary windings amounting to several hundred volts. Since the coil is a basic transformer, a pulse of up to 50,000 volts moves across its secondary windings. The precise amount of voltage is determined by the spark plug's requirement to fire, which can be anywhere from 5,000 volts or slightly more depending on the condition of the spark plug, the gap, and what is happening inside the combustion chamber. This high current is carried from the coil's high tension terminal, through the coil wire, and to the distributor. The distributor cap sends the current to the rotor, which in turn sends it back to the distributor cap sepal plug wire terminals for each cylinder in a timed manner. The spark plug wires then carry the voltage to the spark plug where the current amps the gap, creating a spark inside the combustion chamber. An ignition box is an optional remote unit that can boost the amount of voltage or create multiple sparks for a stronger, more calculated spark event."
Many hot rodders don't think twice about their ignition system as long as it works. However, as engine rpm increases, the ignition system has less time to light the air/fuel mixture. Consequently, the spark must occur earlier in the power stroke in order for it to have sufficient time to ignite the air/fuel mixture properly. "We must remember that when the spark plug fires, there is not an explosion, but rather a controlled burn. If the mixture truly exploded, the pistons and rods would also explode," says Don. "This controlled burn takes a certain amount of time to complete and as rpm increases, the burn process must start earlier. The burning mixture expands, creating the energy needed to force the piston down against the crankshaft to make power. Peak cylinder pressure occurs between 10- to 20-degrees after top dead center (ATDC) depending on the design of the piston, combustion chamber, and camshaft timing. Since the amount of burn time is relatively stable, we can see that the spark must start earlier for the burn to take place in that same window of 10- to 20-degrees ATDC as rpm increases. All ignition systems have various forms of advance mechanisms in them—either mechanical or electronic—to allow the spark to occur earlier based on rpm or engine vacuum."