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."
What's the Point?
Although points-style ignition systems have served the automotive community faithfully for many years, they have numerous shortcomings. The most obvious is that regardless of whether the subject at hand is a performance vehicle or a grocery getter, ignition points wear out. "The points operate mechanically with a rubbing block that rubs on a small cam in the distributor. This rubbing block wears, which changes the timing and the point gap, altering both the performance and the amount of spark available," Don explains. A points system also requires a condenser, which prevents mini-arcing when the points open and close. Without the condenser, this mini arcing would not only wear the points out faster, but it could also cause the primary winding to collapse across the points. This would weaken the spark, so the condenser absorbs the initial shock of the primary winding and delays it just enough for the energy to travel to the secondary windings, creating spark at the spark plugs. In essence, the condenser is a capacitor that wears out from absorbing all this energy millions of times.
Much like the valvetrain in an engine, the mechanical components that comprise a points system are prone to float and bounce. As the points open and close, they rely on a flat spring to keep them in contact with the cam. This keeps them opening and closing at the right time and with relative precision. As rpm increases, however, they reach the limits of the spring, resulting in float and bounce. "Float is where the spring can't keep up, and the points don't close all the way, causing misfires. Bounce is when the spring is over-stressed and the rapid opening and closing cycles causes the points to bounce back open, creating more misfires as the coil is rising and collapsing at the wrong times," says Don. "To combat this, the PerTronix Ignitor system uses a Hall Effect sensor that replaces the troublesome factory breaking points. The sensor is essentially an electronic switch not limited by rpm or mechanical shortcomings. There are no parts to wear out, so in a healthy electrical system, the Ignitor can operate indefinitely. By not having the problems of points arcing and condenser failings, combined with improved control over the breaking of the current to create the collapse of the magnetic field, a stronger spark is the result. A strong spark is the product of the magnetic field collapsing both quickly and powerfully, and that is something that a Hall Effect sensor does much better than a points system."
Ignitor II and III
"PerTronix's original Ignitor system, which has been on the market now for 40-plus years, is a basic Hall Effect sensor that replaces the mechanical switching of points to an electronic switching system. In contrast, the Ignitor II has built-in reverse polarity protection and over-current protection that shuts down the system, preventing component damage if the key is left on without the engine running. Additionally, the Ignitor II units sense the coil current level and use a powerful micro controller to adjust the dwell through PerTronix's patented Adaptive Dwell technology. The Ignitor III takes the features of the Ignitor II even further with the addition of a multi-spark feature and a digital rev-limiter built into the module. At PerTronix, we call this ignition box performance without the box. Additionally, the Ignitor II has a built-in four-degree spark retard during start up to ease the start-up stress in high-compression engines."
Sometimes, one spark isn't enough, which is why many aftermarket ignition systems feature multiple spark technology. "Introducing multiple sparks ensure that the all of the air/fuel mixture inside the combustion chamber gets burned for maximum efficiency and peak power. Unburned fuel is wasted energy that can also contribute to decreased power, higher emissions, and hotter running temperatures," says Don. "Unlike most multiple-spark units on the market, the PerTronix Second Strike ignition box and Ignitor III module deliver multi-spark operation from idle through redline, not cutting out at lower rpm. This is done through complex electronics and specialty low-resistance ignition coils that allow for the rapid charge time required to accomplish multi-spark performance through a broad rpm range."
Adaptive Dwell Technology
"The Ignitor II and III both utilize adaptive dwell technology. To understand what is it and how it works, we first need to define dwell and how it can impact performance. Dwell is the time that the points or the electronic module in an ignition system are closed, and the coil is charging. Standard ignition systems have a fixed dwell angle, meaning that the coil is charged for a fixed period of time during the engine cycle. As rpm increases, that dwell angle has less and less time, so the coil gets charged less per spark event, resulting in a weaker spark. At high engine speeds, a weak spark often becomes the limiting factor for performance and even causes misfires.
"Using Adaptive Dwell Technology, the Ignitor II and III sense the time it takes the coil to charge up to peak current. They use this data to schedule the coil turn-on time so that peak current level is reached just prior to spark for maximum energy without heat buildup, increasing coil and module life. This way they can adapt to any coil that they are connected to. When connected to a stock coil, adaptive dwell maximizes ignition system efficiency, but the real advantage comes when it is used in conjunction with a low-resistance PerTronix Flamethrower II or III coil. Low-resistance coils charge up quickly, and would overcharge and burn up at low rpm in a stock system. The adaptive dwell of the Ignitor II and III keeps the charge time in check at low speeds, and the fast charge time of the Flamethrower II and III coils keeps the spark energy high, much further up the rpm range. The result is a system that works efficiently at low rpm and delivers full spark energy at high rpm."
Flame Thrower Distributors
Although replacing the breaker points in a stock distributor vastly improves ignition performance and durability, aftermarket distributors such as the PerTronix Flame Thrower offer many advantages. "PerTronix Flame Thrower distributors are designed from the ground up to be a substantial improvement over OEM points distributors. They feature precision machined bodies, and tempered distributor shafts that have low torsion displacement for more accurate timing," says Don. "The shaft's upper ball bearing and extra long oil impregnated bronze lower bushing work together to reduce friction and high-rpm vibration, thereby extending longevity. Likewise, the timing advance mechanisms are highly refined and are fully adjustable so the owner can tune the advance curve to the characteristics of the engine. In contrast, when you install a PerTronix Ignitor in a factory original distributor you are gaining all the electronic benefits described above, but if the distributor is worn or not performance oriented, it will not allow for all the performance upgrades Flame Thrower distributors have to offer."
To accommodate street cruisers and racers alike, PerTronix offers both street and race versions of its Flame Thrower distributors. "Although the basic body and shaft of the race and street Flame Thrower distributors are the same, the Race version boasts many upgrades that include TIG welded timing advance mechanisms for superior reliability at high rpm, oil holes for improved shaft and gear life, and a crankcase pressure relief path," Don explains. "Other features include a race-only 7.2-amp module and a 50,000-volt coil, which when compared to the street/strip distributor produces 42 percent more energy with 46 percent faster spark breakdown time. This allows for 48 percent more peak current to reach the spark plug."
"In an ignition system, the purpose of the coil is to multiply the 12 volts supplied by the battery into tens of thousands of volts. A coil is a coupled inductor, consisting of two windings around a common magnetic core. An inductor resists changes in current, so when you switch it on it takes a while for the current to start flowing. More importantly, when you switch it off quickly the current keeps flowing for a bit. This creates a temporary charge across the primary coil winding, bringing the voltage up to several hundred volts. Since the primary and secondary windings are magnetically coupled, their voltages are related by the turn ratio between them. The ratio between the two windings is usually around 100-to-1, so the several hundred volts on the primary side become tens of thousands of volts on the secondary side. At some point, the secondary voltage gets high enough to ionize the spark plug gap, and at that point all of the energy stored in the coil dumps across the plug in the form of a spark.
"PerTronix Flamethrower coils are among the highest quality ignition coils you can buy today. We perform an enormous amount of testing to ensure that each coil meets our quality standards. The resistance and inductance values are selected to match our different modules. In PerTronix's published tech data, you will find where we recommend different resistance values depending on the application. Additionally, PerTronix offers E-Core coils that are far more efficient than conventional canister coils for even stronger spark performance."
The OEs have rapidly transitioned over to coil-on-plug ignition systems. While the benefits of these systems are obvious, they come with drawbacks as well. "These systems generally eliminate the conventional distributor altogether and control spark and timing completely electronically. By doing this, you eliminate the mechanical trappings that now allow more control and reliability in the spark management," says Don. "By getting rid of the distributor cap, you eliminate the possibility of crossfire within the cap. Individual coils also allow for different dwell times, which can increase spark at higher rpm and let the coils run cooler for longer life. Of course, there are downsides as well. These systems are much more complicated and not easy to retrofit to pre-computer cars. Performance upgrades can be considerably more expensive due to needing to replace eight coils instead of just one."
Spark plug wires are yet another part of the ignition system that are often taken for granted. Although they may look simple, there's quite a bit of technology beneath the surface of the wire that distinguishes a quality aftermarket plug wire from stock plug wires. "Modern spark plug wires are light years ahead of what was used years ago. In the case of PerTronix Flame Thrower wires, we use a dual-current path for both reliability and redundancy," Don explains. "The primary path is a spiral wound stainless steel alloy and the secondary is a carbon-impregnated fiberglass center core. They feature a low 500 ohm per foot resistance that allows more energy to reach the spark plugs. They also boast a 50kV EPDM (Ethylene Propylene Diene Methylene) rubber inner insulation for superior heat resistance and prevention of arcing and voltage leaks, which can cause unwanted radio-frequency interference."
Many 1960s muscle cars did not come with rev-limiters from the factory, but fear not, PerTronix offers a way to add a digital rev-limiter without having to install an aftermarket ignition box.
"The purpose of a rev-limiter is to protect the motor during any instance it could over rev, such as during a burnout or a missed shift. The PerTronix Digital Rev Limiter (and the Ignitor III module) are adjustable units that have a far superior rate of accuracy compared to the analog chip-style systems used in other rev limiters," says Don. "It will hold the resolution to within one percent, and it can be adjusted in 100-rpm increments. It is a random, spark-stealing type of rev limiter that provides superior control of rev limits and a rapid response time to over-rev limit events, preventing engine failure and the spark plug fouling that's common with repetitive, stealing-type limiters."
While many stock-style ignition systems inductive spark technology, aftermarket ignition systems usually employ capacitive discharge technology instead. "Inductive and capacitive discharge spark systems both have their advantages. Capacitive sparks from CD ignition boxes are very hot, but also very short in duration," Don explains. "On the other hand, inductive sparks from conventional ignition systems are not as hot, but they last longer. PerTronix Second Strike ignition box provides the best of both worlds, featuring a long inductive spark followed by a powerful capacitive second spark. Another nice feature of the Second Stroke box is its crank angle offset adjustment feature. Every engine is different, and the crank angle offset adjustment lets you optimize the ignition system by setting the split between the sparks. You can adjust the split from 2-degrees to 18-degrees, in 2-degree increments. Most engines make best power with between four to eight degrees of crank angle offset, with higher compression engines generally requiring less time between spark events than lower compression engines."