Standard kawi igniter makes 0,8 millisecond spark when using standard spark plug and have managed to push the spark through at ten bar only under 1500 rpm above that, energy from coil have gone over ceramic or debris on it in to the ground. Already at this stage there was no spark in the chamber at all but the plug outside had spark. Between 1500 and 7500 rpm dwell time reduced from 10 to 2 milliseconds. I remember long ago I had made similar test and the figures varied slightly from that, on different igniter, maybe the setup was little different or due to lower supply voltage. After installing iridium spark plugs things got slightly better.
Like said before, some people have feeling that the performance of the engine is better after installing iridium plugs. I personally think that this is absolutely true, I'll explain my observations. Lets take a look at how spark is "born". The charge from ignition coil is moving towards its destination, the electrodes of the spark plug. Only to find in there a gap, instead of closed circuit but the energy must go somewhere so it starts to ionize the gas in order to build plasma and be able to escape. In order to ionize the gas high voltage must first build the field of energy around electrode to free electrons from the atoms which will then become ions and when there is enough of theme to bridge the gap ionization process rapidly starts. Now I stop. We look back to standard plug with big electrodes and compere to iridium plug electrode form, which i significantly smaller so to my understanding the energy required to create force field to break electrons to ions on small electrode is a lot less than on the large electrode. I got this idea once when building stainless steel model of ball gas tank form refinery. I was welding tiny stuff with barely 15 amps and i notice when my electrode was little blunt i could just hold the arc alive before I stuck it on to work piece, but with very very sharp electrode it was merely a task, so you see the similarity ? Also on the example from above at 1500 rpm there is just not enough energy to ionize the gas with large electrode probably because the surface is so big and you need more force to rip electrons free and with tiny one everything is more concentrated. Yeah this are just some thoughts when I'm welding at work
Kawboy. Any ways all this information I write here are being collected over the time from various sources and literature, also I like to say that I'm by no means any professional electrician electronic or engineer working for development sector of any kind. I'm making my own experience in various fields, building stuff, traveling, being a dad of two or even cooking. All of this is a challenge I'm happy to take on any time, and like I wrote before learn from it and share the experience gained. So here I am now, talking to you about breaking electrons free from the gas atoms. Anybody want to add something here or have further questions regarding iridium plugs ?