what are everyone's thoughts on ignition add-on stuff such as the multi-spark ignition boxes offered from MSD, Crane, etc...
I bought my first MSD (model 5, the cheap one) back in '79. Transferred it from vehicle to vehicle until it failed around 1988. Went back to MSD for repair, and I still have it, it works, but it's not being used.
I put a used MSD 5C (same guts as the plain "5" but with a
Chrysler-style molded-5-pin connector that the Chrysler electronic ignition plugs right into) onto a '67 Dart I converted to electronic ignition. Worked great until the car got totaled, and I sold the MSD to another Chrysler-lover.
I put a MSD 6AL (the original kind) on my hot-rod El Camino. Works great. Still have it.
I had a MSD 6T that I bought used on my '88 K1500 for a few years. The box failed, and
I never bothered to get it fixed because the truck doesn't run any different with or without it.
I've even got a MSD "store display" unit I use for testing those boxes. I paid about what a MSD 6 cost at the time, and the display included the MSD 6 and a MSD coil that failed not long after I got it. The black knob on the top adjusts the spark gap above the coil. You can see a pretty-hefty "C" shaped spark leading from the coil boot to the tip of the brass ground electrode.
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I've got half-a-dozen MSD spark boxes stuffed in a drawer in my shop. Far as I know, they all work except for the 6T. I've come to the conclusion that if they make a radical difference in the way a street-driven engine runs,
you're pretty lousy at carb tuning. These spark-boxes are great at covering-up idle misfire from improper fueling at idle. Beyond that, I've cooled to their use. MSD has quality issues and has for years. And don't get me started on ignition coil failures due to moving production first to Mexico, and then to China.