[cycleguy55]

Originally Posted by olddog

You need voltage to make a spark jump across air. The higher the voltage the more powerful the spark, and the longer distance it can jump. You start adding things to the air, like fuel, you need more current to push the spark across the gap. All the theory I lack, but here are some takeaways.

Cold weather cold start needs a hotter spark to light the poorly vaporized fuel.

A weak spark can cause a lean engine to backfire. Richen the fuel or a hotter spark will stop the backfire. The hotter spark is usually the better solution.

Boosted engines need a hotter spark.

If you have a decent ignition system that is hot enough to make the engine run well, adding a MSD gains no power. If you do gain power, it was because your ignition system wasn't good enough.

MSD has often been proven to retard timing at high rpm. One chap measured 20^ timing loss at 10,000 rpm, but didn't state at what rpm this starts to occur. I expect it is above 7000 rpm. It's suspected that it has to do with the time require to charge or discharge the capacitors.

I do believe MSD has enough power to stop your heart if get into it and get a good ground where the current flows across your heart.

As for the multi spark at lower rpms, it may do something, but it seems to me that a good hot spark that lights the fuel shouldn't need a second spark. If the 2nd spark does in fact light the fuel in a different spot, you now have two flame fronts heading toward each other. At high load, I could see this collision causing detonation. Just thinking out load.

Personally I have 1990 factory EFI that is controlling the spark with a distributor. I have never experienced anything that makes me believe I need anything hotter. I am a believer in the don't fix it, if it isn't broke camp. Never add complexity to solve a nonexistent problem, unless there is a real tangible benefit. I cannot tell you the number of threads on this site that fall under "help troubleshoot my broken MSD," but it is a big number. I do not recall a single thread of I just put a MSD in and it performed something wonderful.

That said the 60's point system are not up to snuff, but I expect there are things that are good enough, other than MSD.

I have no doubt there could be timing issues with an ignition box. I'm not running 10,000 RPM, or even 7,000, but I do know there were huge differences in timing when I replaced an analog MSD 6AL with the digital equivalent.