Some may argue that output voltage of an ignition system does not have to exceed 35,000 to 40,000 volts as normal demand doesn’t exceed this. The voltage required to initiate a spark across a spark plug gap depends on a number of conditions including, but not limited to, cylinder pressure, fuel mixture, and spark plug gap. Once the voltage to jump the gap is reached, a spark is formed and current flows creating the mass of the spark. Increases in cylinder pressure and spark plug gap, as well as less than ideal mixture ratios (either too rich or too lean) will increase the voltage required to create a spark. In more simple terms, when you twist the throttle, requirement goes up. If you increase your engine’s load while pulling a hill i.e. more fuel volume enters the cylinder (upping pressure), requirement goes up. If your plugs wear and the gap burns larger, requirement also goes up. As well, any changes that you voluntarily make such as exhaust modifications, bigger fuel injectors, camshaft changes,increased compression ratio or increasing your plug gap to get a bigger spark, all increase the firing voltage requirement.
A number of misconceptions have been made over the years. Let’s take a minute to review a few popular ones. ” Too hot a spark will burn holes in your pistons ” – not true. Pinging or detonation caused by poor fuel grade, incorrect fuel mixture, or incorrect ignition timing cause this kind of damage. ” Too hot a spark will cause your engine to run too lean and run hot ” – not true either. Fuel mixture alone dictates rich or lean. Too rich and combustion temperature goes down, too lean and it goes up. Too weak a spark can cause a mixture not to burn well leaving behind too much unburned fuel. However, having close to complete combustion of a proper mixture is not harmful. ” Any spark will do to run an engine ” – partly true. If the spark can initiate combustion, the engine will run. Beyond that it is a matter of efficiency. The fact is that there is a finite amount of time for a mixture to burn before the exhaust valves open. As well, the higher the RPM the shorter this time becomes. Here is an analogy to demonstrate this. If you were to take a sheet of paper and light it with a match, the paper will burn in ” x ” amount of time. If you were to use a larger flame to ignite the same sheet of paper, the subsequent larger flame front would consume the paper in a shorter period of time. Both methods will burn the paper no question. But like an engine, if you only have a finite amount of time to complete a burn, you would choose the larger flame. This is not to imply that fuel burns slowly in an engine. Fuel actually burns very quickly, however we are talking about only milliseconds of available time to have a complete efficient burn in a cylinder between valve openings.