I have no experience with MSD, but do have a dumb question. How do they control the dwell time?
The reason I ask, is that years ago (about 1980) I had a "semi-transistorized" ignition (used points to fire an igniter) which was good up to 9000 rpm or so. The problem I had, strangely, was at idle or very low rpm. With the turn signals on, the idle speed would rev up and down, and my timing light showed the advance drifting back and forth. Insufficient current was changing the dwell time for the coil and igniter.
It was a corroded wire harness feeding the igniter power, combined with low alternator output at low rpm.
so....fast forward to 2000 and a Pectel T2 fuel injection on a turbo banger. The actual timing, at the plugs, would not stay stable under load, and it just wouldnt rev up during high cylinder pressures. Pectel told me to go get Ford Ranger coils and wire them "Menard V6" style (small 6-volt battery in series to the coil 12V terminal). That worked and solved the problem of not enough dwell to build enough voltage in the coil secondary to get the spark off on time. In fact....it was pretty late, I suspect until cylinder pressure let down enough to make the jump!
Might have been a fuel vaporization issue, also, because you can't spark on time if the spark plug is surrounded by mostly compressed air. The timing light only flashes when the spark actually jumps, not when the ignition asks for a spark event. Anyway, hot coils and 18V took care of whatever was going on.
I still dont get it, but their recommended fix worked just fine.
JimL
PS: The Ranger coils held up to 18 volts ok, when the engine spent most of its time at high rpm. They were the coils from about '96 or so, when it took a lot of spark to fire lean across a wide gap. I dont think most coils will put up with that, but those never failed us.