With simultaneous ignition systems, two cylinders are matched according to the position of the piston. This has the effect of simplifying the start-up time and reduce the level of voltage required for the secondary circuit. For example, let’s look at detail what happens in particular in cylinders 1 and 4 in a V-6 engine. We know very well that in the vast majority of all V-6 engines almost all the brands, all the years the firing order will always be the same: 1-2-3-4-5-6, with some rare exceptions. Also know that these engines cylinders 1 and 4 are twinned, i.e. that both Pistons occupy the same position (the two are at TDC and PMI at once), they move in unison, however, they are working in different careers.
When is the 1 cylinder on the compression stroke in the first revolution, the cylinder 4 is on the exhaust, vice versa the next revolution in stroke and so on while the engine rotate. (This is a fundamental concept of basic mechanics; if the reader does not relate the driving phenomenon that we are describing, I invite you to refer to the literature and courses in video that best serve you for newbies in mechanics). High voltage generated in the secondary winding is applied directly to each spark plug. The way that happens is in the following manner: in one of the two spark plugs, passes spark from Center electrode towards the side electrode, and another spark plug spark for from the side electrode to the Center electrode. Typically, the spark plugs that are recommended in this type of arrangement are tip of Platinum, for the characteristics of high strength and ductility of this material. The voltage necessary to put the spark discharge is determined by calibration of the spark plug and the compression pressure. If both spark plug electrode calibration is equal, then the voltage is proportional to the download required pressure inside the cylinder to make it happen.