Let’s talk ignition
As far as ignition systems go there’s not much to know. Spark plugs, wires, cap and rotor are about it aside from the ignition coil itself. However there’s a common factor at play and from a performance standpoint it’s somewhat useful to have a deeper understanding for both performance and diagnostics when it comes to misfires.
The ignition coils used on most cars today haven’t changed all that much in the last 50 years. A simple set of windings that when provided electricity creates a magnetic field that when collapses is amplified and creates enough voltage potential that it can jump a gap between two points. For our purpose with this article that’s as far as we’ll go with the understanding of transformer (ignition coil) fundamentals. Let’s instead focus on the bigger picture as it relates to misfires, specifically those that occur from increase boost and power development.
Before we go any further let’s talk about Voltage and Amperage. To get a more easy to understand definition of these two let’s simplify a bit and defined Voltage as the Velocity of the electrical energy and Amperage as the Amount of electrical energy. Voltage=Velocity, Amperage=Amount. This is a more basic understanding of electricity but will serve well for the following discussion.
Let’s start with some givens.
1. An ignition coil that is provided a given voltage and amperage can produce a given amount of multiplied electrical energy (spark energy).
2. The larger a spark gap the more Voltage (Velocity) is needed to jump that gap. This voltage is referred to as ionization voltage and is the minimum necessary for the spark energy to jump the gap on the spark plug and ignite the mixture.
3. The more boost pressure in a given engine the higher the ionization voltage requirement (the voltage necessary to jump the gap)
4. The richer the mixture the higher the ionization voltage requirement.
The reason that a higher voltage is needed with higher boost and richer mixtures is that the more molecules of air/fuel there are in the combustion chamber the more molecules there are in the way of the spark as it tries to jump from the spark plug electrode to the ground strap. At some point we can end up requiring more spark energy to bridge the gap than the ignition coil can provide. This is what is referred to as “Spark Blow out” or more properly defined as “Boost misfire”.
To combat this you have two basic options. First is to reduce the spark gap (typically by 0.006”)
Second is to install a larger ignition coil. However to properly maximize a larger ignition coil the time it takes to charge the coil (Dwell time) must also be increased. Increasing dwell time can be done either through a change to the ignition dwell map in the ECU or through an aftermarket ignition controller like the MSD 6A which is fairly popular in the aftermarket.
As a side note, I frequently run into ignition misfire issues from cap/rotor failures that from a visual inspection seem fine but after replacing all other ignition components the misfire still exists. Once the cap/rotor have been replaced then the misfire is suddenly gone. So even if they look ok visually if there’s more than 30K on those parts, consider them ready for replacement!
The harder we push our cars with respect to performance and power the more we are requiring of the supporting components. Make sure you’ve given your car the attention it needs to perform to its full potential.
As a final note, it’s been a number of weeks here at MVS Fast Fridays and we’re interested in your feedback, so if you’ve got ideas or a request for a Fast Friday article email us and let us know!
Robert Lucky Arnold