Modern Ignition Basics - Turbo Magazine

The ignition system is one of those entities that is overlooked, taken for granted and passed by until something goes wrong with it. Consequently, many enthusiasts don't fully appreciate the down-in-the-trenches job it does day in and day out. Further, many do not realize when it is time to step up the power of the ignition system.

Ignition: The Prime ObjectiveThe prime objective of the ignition system is to energize the spark plug to the point that a spark jumps the gap between the electrode and the strap. It must also do this at the correct moment in the cycling of the engine. Typically the plug fires near the end of the compression stroke just before TDC. The timing of the spark event is a critical piece of the tuning puzzle and the exact moment depends on many variables.

The ignition system can be divided into two sectors. The transition point of this division is the coil and the focus is on the type of energy in the system. From the coil back to the battery the system is low voltage. This portion, called the primary side, is made up of the ignition key circuit, the battery and the coil input wire.

The coil is where all the magic happens. The 12 volts or so input by the battery are supercharged to 20,000 volts or more then released. The hot wire on the coil is where the secondary side of the system starts.

From the coil the next link in the chain is the distributor, which does what its name implies; sees that the 20,000 volts are shot from the coil to the correct spark plug. The distributor houses a triggering device, which rotates via a shaft in the distributor that is driven by gears on the camshaft. The distributor shaft is how the distributor gauges the cycling of the engine. The triggering device itself can be mechanical points, magnetic pickups or a Hall-effect device.

Points complete the electronic circuit (firing the 20,000 volts) by physical contact. Magnetic pickups use magnetic fields to initiate the firing of the system. However, in many cases the magnetic pickup array is incorporated into the crankshaft and these setups are known as external triggers because they are not contained within the distributor body. The external magnetic pickup uses crankshaft rotation to determine the cycling of the engine. The Hall-effect device is the least common approach however they can be used in a number of different ways.

We have explained the "how" of trigger but it is the "when" that is most critical; especially when engine speed, load and power modifications come into play. If the spark hits too early during the compression stroke the air/fuel mixture may not be properly atomized, which can result in detonation (also called pre-ignition) because the mixture burns unevenly and too soon before TDC. This early burn can lead to engine failure by putting too much pressure on the piston and rod while the piston is still moving upward in the cylinder

Firing the plug too late means there is less time for combustion and a partially combusted mixture means only partially realized power. Also, the timing demands of the ignition change as engine speeds increase so distributors use a mechanical advance that cleverly uses centrifugal force to change the timing dynamics of the system.

The Distributor Is Dead; Long Live Distributorless Ignition SystemsThe modern ignition is a distributorless ignition system (DIS) that was pioneered in a performance application on the 1986-87 Buick Grand National.

The distributor was ditched for a number of reasons both economical and performance related. The distributor shaft rotates via helical cut gears on the camshaft, which takes its cues from chain driven gears on the crankshaft. The meshing of these gear teeth is not conducive to precise timing. Factor in the exceedingly high redlines of modern performance engines and any shortcomings are further magnified.

The OEMs began to rely on electronics more and more in the 1980s. This reliance was driven more for emissions reasons rather than performance. So as engine control systems evolved, the distributor was asked to do less and less until all it did was send the energy from the coil to the plugs. The advent of multiple coil packs meant the ECU could team up with these high-voltage packs directly and it was game over for the distributor.

The DIS setup consists of a two-tower or four-tower wasted spark setup and individual coil-per-cylinder systems. In wasted spark systems the coil fires two cylinders at a time; one for combustion the other while it is the exhaust stroke which has no use, nor does it hurt anything; hence the term 'wasted.' Coil-per-cylinder setup have the advantage of firing for one cylinder which means there is more time to fully charge the coil in between discharges, which is increasingly important as production engine redlines edge closer to 8000 rpm and race motors don't hesitate to spin to 10,000 rpm or higher.

Inductive Versus CD IgnitionMost factory ignition systems, from antiquated breaker points to modern coil packs, are inductive ignitions due to their simplicity, reliability and inexpensive production. "For stock applications this is adequate at best," says Todd Ryden of MSD Ignition. "But when it comes to performance the factory inductive ignitions fall short. The primary weak link of an inductive ignition is because the coil serves double duty. The coil must act as a step-up transformer to create a higher voltage spark, plus it needs to store this power until a trigger signal releases it. As engine rpm increases there isn't enough time to completely step-up the voltage before the ignition is triggered resulting in a weaker spark. This can result in a low-voltage spark that may not be enough to light the fuel mixture in the cylinder which will result in a misfire and loss of power.

"Most of the high performance ignition systems you see use Capacitive Discharge (CD) technology. A CD ignition control has several benefits that not only will improve the performance of your car, but also the driveability. For starters, a CD ignition is capable of producing full power sparks throughout the engine's entire rpm range with no fear of a weak spark at the top end. This is because it draws its voltage supply directly from the battery and uses a custom wound transformer to step up this voltage to over 480 volts and higher. This voltage is stored at full strength in the ignition's capacitor until it is triggered. At that point, all of the voltage is dumped into the coil where it is stepped up again and capable of reaching from 30,000-48,000 volts depending on the coil!

"Another benefit of most CD ignitions is that they produce a series of sparks at lower rpm. Up to 3000-3300 rpm these controls are capable of delivering several sparks to each plug rather than just a single spark thanks to the quick rise time and power of CD circuitry. This series of full-power sparks creates more heat in the cylinder resulting in improved combustion of the fuel mixture. The results are an improved idle, quick starts, crisp throttle response and improved top-end performance."

Factory Versus Forced InductioBy introducing a powerful spark to the air/fuel mixture the combustion event becomes much more efficient resulting in more downward force on the piston which adds up to improved overall performance. When you consider all of the different variables that affect the combustion event in the cylinder it is easy to see that achieving complete combustion of the air/fuel mixture every time is not going to happen.

There are plenty of variables that affect the quality of the combustion in the cylinder ranging from fuel quality, the condition of the spark plugs and wires, driving habits, air flow, temperature, even the design of the head and intake manifold can work against complete combustion. Imagine how the dynamics change when nitrous, a turbo or a supercharger are added to the mix.

"With boost pressure," says Ryden, "all of a sudden, the air/fuel mixture is being forced into the cylinder and this dramatically increases the cylinder pressures under combustion. This makes it tougher for the spark to ionize, or jump the gap. This is where the need for high voltage arises. The need for an ignition that can supply the extra oomph to get a spark to flow across the gap."

"Not only will a CD multiple-sparking ignition produce benefits, but remember that spark plug wires and the coil both have important roles in the ignition system. Once again, OEM wires and coils are designed for the masses and they leave a lot of room for improvement.

"For instance, factory plug wires will have resistance values (the measurement of the resistance to the flow of electricity) upwards of 5,000-10,000 ohms per foot! The MSD Super Conductor plug wire has less than 50 ohms per foot-that means more energy can make it to the spark plugs when it is needed most. A lot of people look at ignition boxes as race-only pieces but that is just not the case. In fact, a lot of these ignitions are legal to install on pollution-controlled engines!"

Real World Performance UpgradesWhen do you need an ignition upgrade? Unfortunately that question has no singularly correct answer. The basis of the answer starts with the capacity of your stock ignition, the condition of the system on your particular engine, and the intensity of the mods going into your car. If you are adding forced induction to a naturally aspirated engine the added cylinder pressure could very well overwhelm the OE ignition system. If you have a factory turbo car and are upping the boost a few pounds you should be okay but if the plan is to run a 100-shot of nitrous an upgrade may be in order.

The first line of ignition upgrades should consist of amplifier boxes for inductive ignitions that not only add to the voltage going to the coil but speed the coil charging time, which helps keep the energy up at high revs. Additionally, an upgraded canister style coil with more windings will generate more power on the secondary side of the system.

The next step is CD ignitions; as discussed earlier, most likely the first step for a turbo conversion build-up or any mod that greatly increases cylinder pressures. From here coil upgrades and amplification boxes for multi-coil and individual coil systems kick in. Some of the top-end boxes in this range are highly programmable, controlling everything from simple rev-limit programming to individual cylinder spark tuning. The key is to consider the effect your proposed modifications will/may have on the ignition system and make upgrades where needed.