The dwell control dialog alters the coil charging time (dwell) for Speeduino's ignition outputs. Care should be taken with these settings as igniters and coils can be permanently damaged if dwelled for excessive periods of time.
From the April 2017 firmware onwards, dwell will automatically reduce when the configured duration is longer than the available time at the current RPM. This is common in single channel ignition configurations (Eg 1 coil with a distributor) and in particular on higher cylinder count engines.
Note: Both the running and cranking dwell times are nominal values, assumed to be at a constant voltage (Usually 12v). Actual dwell time used will depend on the current system voltage with higher voltages having lower dwell times and vice versa. See section below on voltage correction
As the system voltage rises and falls, the dwell time needs to reduce and increase respectively. This allows for a consistent spark strength without damaging the coil/s during high system voltage conditions. It is recommended that 12v be used as the 'nominal' voltage, meaning that the Dwell % figure at 12v should be 100%.
The correction curve in the base tune file should be suitable for most coils / igniters, but can be altered if required.