Hi, I've been sitting on this for a long time. A long time ago, some of us on the LCML were talking about putting a book together on LC electronics. I was going to do a chapter on ignitions. But that is not going to happen. I see often people wanting to know about which ignition to put in their LC, including a recent thread, which made remember I had this stuff, and now that I'm on a forum that I can put pictures on... Now, I'm not claiming to be an expert, but I did take some automechanics in High school 30 years ago, and spent a year analyzing ignitions on a Sun scope. Ignitions back then are very different from ignitions today, but the basics is still the same. So here is some info, take it or ignore it as you see fit... To start, in this pucture you will see two traces, the lower one is the primary ignition circuit: battery, ballast, + side of the coil, points, condensor. You will see the points open, higher voltage, and the points close, lower voltage. The upper trace is the secondary circuit: coil high tension lead to spark plug. Focusing on the part of the traces that we are most interested in, the spark... You will see at the instant the points open, there is a spike in the secondary circuit. This is the energy dumped to the spark plug to bridge the gap with an arc. The larger (higher voltage rating) the coil, the larger this spike will be. Then you will see a changing (fading)voltage level, this is the energy depleting across the spark in the plug gap. Then you will see another spike. When the fuel actually ignites, the blast will "blow out" the spark making the plug gap an open again. The length of this second spike is an indication of the energy remaining in the coil after ignition has occured. My contension is that the length of that second spike is a valid measure of the ignition. If there is no second spike, then we don't know if the fuel ignited, or if the energy ran out, and there was a miss fire.