Spark plays a very important role in the engines performance but is often overlooked. So let’s go over the basics of the Coil over plug “COP” system as well as the different types of components that are crucial in the success of our builds. Coils come in many shapes, sizes and are made by several manufactures but to keep it simple we will just talk about the difference between the most commonly used; Smart and Dumb coils.
Smart Coils have the igniter/PTU built-in, so it will not need a control or igniter just an ECU signal to function. These coils have their own power, ground, and signal wire for the igniter and are a great option on most applications with room to grow.
Dumb Coils do not have the Igniter/control box built in so it needs some form of CDI/PTU amplifier to work properly and can sometimes add up to a hefty price tag if you’re shooting for higher numbers.
*Warning the following is extremely boring technical stuff written by an engineer with zero social skills:
The operating principle of a power transistor unit (PTU) or similar devices (igniters) is as follows:
The PTU and comparable devices are necessary in older cars to isolate the ECU’s fragile low voltage electronics from the high voltage transient circuits that occur when a spark plug discharges. By using transistors to switch the load, the ECU can be completely isolated and thus, protected. For those that don’t know how transistors operate, you can think of them as near perfect switches, similar to relays. The difference is that a transistor is made of solid state technology and can switch a circuit faster than a relay, while being more reliable. Knowing that spark plugs put out around 20kV, you might ask yourself where the voltage comes from…
Before we answer that, let’s talk about modern ignition systems. In these types of systems, the PTU/ igniter modules are built into the coil packs for cost and reliability reasons, but they operate under the same principle. The ECU sends the coil an inverse 5V square wave trigger where the pin is held high (5V) until it is pulled low (grounded) to fire.
In both types of ignition circuits, after the PTU/igniter part, comes the actual ignition coil. What an ignition coil consists of is actually a fairly simple transformer. An electrical transformer is a device that can convert low voltage to high voltage, at the cost of current, or vice versa, low current to high current at the cost of voltage, using Ohm’s Law (Voltage = Current * Resistance and Power = Voltage * Current). When the ECU sends the signal to fire the spark plug, this creates a disturbance in the magnetic field made by the transformer, and the result is the spark plug firing.
So… wrapping it up, the main step up from 5V logic in the ECU to 12V happens in the PTU/ igniter part of the circuit, and the major step up from 12V to 20kV happens in the ignition coil via the transformer circuit described above. The large discharge of electrons upon firing has nowhere to go but the path of least resistance, and since the spark plug is made of ceramic, non-conductive material, the electrons jump the gap in the hook part of the spark plug and into the nearest ground point, the engine block, through the threads in the spark plug. This is also why it is very important to ground the engine to the chassis, and why bad grounds affect spark!
In short, don’t skimp and leave your twenty year old system ‘til last, address it early on and you will be much better off.