Please observe the above animation. Most electronic
ignitions used to date sense crank angle by using a hall effect pickup,
which is a magnetic type sensor. This type of sensor is inherently
unstable & is effected by metal mass, motion, heat & distance
from pickup. In addition most ignitions only sense position once
per revolution. The control system must estimate current engine
speed based on the rotational velocity of the previous
revolution. Sudden acceleration or deceleration will cause
instability. This instability causes internal vibration that can be
observed by the movement seen on the flywheel when using a timing
light. The use of a magnetic type sensor can cause timing to be off as
much as ±7° giving an overall deviation of 14° or more. With an optical
sensor you are breaking a light beam and light beams do not deviate! In
addition absolute positions are sensed at multiple key points on the
rotor, 90 times per revolution with the new IDS system. The
extreme stability optical systems offer allows the engine to accelerate
at a much greater speed, reduces engine wear, allowing for smoother
operation & transfer of power.
During the intake cycle fuel is delivered via a carburetor or injection system and intake manifold into a combustion cylinder. Both of these delivery systems supply fuel to the cylinder in a droplet form, especially at lower rpm ranges. As the fuel is compressed turbulence in a circular fashion is created due to existing head designs. As the primary spark is discharged the concussion of the explosion combined with super-heating of the combustion chamber causes any remaining fuel to remain as a hot vaporous gas. The flame front due to the rolling turbulence created by the heads moves away from the point of ignition to the face of the piston and to the outer cylinder walls. As the piston nears the top of the compression stroke any remaining unburned vaporous gas is circulated over the spark plug, and a fuel roll stall occurs. At this point a second spark is discharged obtaining a secondary burn of the fuel that in a single spark ignition system would be trapped in the upper portions of the head and during the expansion portion of the power stroke would be unburned and then be cycled out during the exhaust cycle as emissions. With the extreme stability of an optically triggered ignition system in a multi-spark mode a repeatable secondary explosion is possible. Remaining unburned fuel can thus be consumed. This also allows for the ability to add more fuel without fouling the spark plugs and achieve higher torque/horsepower.
Note: The extreme stability of a optically triggered ignition system has the ability to allow the engine to accelerate as much as 30% quicker temporarily requiring greater fuel flow to the carburetor. The ignitions ability to handle enlarged jetting of the carburetor or increased fuel to the injectors means if fuel flow is increased you must maintain a sufficient supply line from the fuel tank to the delivery system by use of an enlarged petcock and supply line or a fuel pump. An example would be that at higher rpm's you may use all the gas in the float bowl of your carburetor and create a lean run situation damaging the engine if fuel supply is not maintained.
Spark plug gap should be made as small as possible,
while still maintaining performance. A wide spark plug gap can cause
hard cold starting, misfires during rich or lean fuel conditions, and
reduction of upper rpm range. To maintain a good secondary spark
(multiple spark) within a wider rpm range it is wise to run a narrower
spark plug gap. It is better to precisely place two stable, consistent
sparks than to fire one wider spark that may cause misfires under
Many things effect spark plug gap settings
Compression Ratio: The higher the engine compression, the more voltage required to fire the plug, and the narrower the plug gap should be.
RPM: The higher the rpm's the less time the coil has to charge to break over voltage or complete saturation. A narrower spark plug gap will help high rpm stability.
Spark plugs with large side electrodes (ground straps) or
spark plugs with split side electrodes are not recommended, they
interfere with the flame front at the point of ignition.
In most cases, it is not until the engine is modified, or the compression is raised significantly, that stock ignition systems and spark plugs begin to show signs of being inadequate. At this point, a variety of factors determine which spark plug will be best suited for a particular configuration. In these modified engines, specific electrode/tip combinations, electrode materials and colder heat ranges can provide measurable gains in power. If your vehicle has had extensive modifications, it would be best to seek the advice of the manufacturer of your vehicle, the aftermarket supplier who manufactured your modifications, or your mechanic.
Modifications that will typically not require specialized plugs (in most cases the factory installed plug will be more than adequate) include adding a free-flowing air filter, headers, mufflers and rear-end gears. Basically, any modification that does not alter the overall compression ratio will not usually necessitate changing plug types or heat ranges. Such minor modifications will not significantly increase the amount of heat in the combustion chamber, hence, a plug change is probably not warranted.
However, when compression is raised, along with the added power comes added heat. Since spark plugs must remove heat and a modified engine makes more heat, the spark plug must remove more heat. A colder heat range spark plug must be selected and plug gaps should be reduced to ensure proper ignition in this denser air/fuel mixture.
Q: Why should I use a resistor spark plugs & spark plug wires?
A: "R" or resistor spark plugs use a 5k ohm ceramic resistor in the spark plug to suppress ignition noise generated during sparking.
You must use resistor spark plugs & wires in any vehicle that uses electronic ignitions or on-board computer systems to monitor or control engine performance. This is because resistor spark plugs & wires reduce (EMI) electromagnetic interference with on-board electronics.
They are also recommended on any vehicle that has other on-board electronic systems such as engine-management computers, two-way radios, GPS systems, or whenever recommended by the manufacturer.
In fact, using a non-resistor plug or low resistance spiral wound spark plug wire in most applications may actually cause the engine to suffer undesirable side effects such as an erratic idle, high-rpm misfire, engine run-on, power drop off at certain rpm levels, abnormal combustion and probable damage to the ignition and/or ignition coil.
Q: Why are there different heat ranges?
A: It is a common misconception that spark plugs create heat. They don't. A heat range refers to how much heat a spark plug is capable of removing from the spark plug body.
Selecting a spark plug with the proper heat range will insure that the tip will maintain a temperature high enough to prevent fouling yet be cool enough to prevent pre-ignition. While there are many things that can cause pre-ignition, selecting a spark plug in the proper heat range will ensure that the spark plug itself is not a hot spot source.