Info on FBO ecu unit

Keep in mind that the max permissable dwell at high RPM isn't very much. At 3000 RPM on a V8, you have 5 milliseconds between spark events. If you give the coil a millisecond to discharge, you have 4 milliseconds for it to fire. Keeping the same 1:4 ratio between discharging and dwell would drop that to 2 milliseconds at 6000 RPM.

Plug in the numbers for an MSD Blaster 2 coil and aim for a max current of 6 amps as a somewhat conservative safe level of current, and you'll find it needs to dwell for 4.9 ms to reach that much current. That 2 ms time at high RPM would only reach about 2.7 ms. At low RPM there is enough time that you would want to stop the charging at a point that limits current. The just isn't enough time to reach high levels of current at high RPM, so at that point any dwell control is aimed at managing the ratio of discharge time to dwell.