Approximately what percentage is the DC voltage value of ignition coil high volts changed to half wave dc through one diode? This is a pulsed wave already, (not AC) either positive or negative output, but fully dc after the diode proper placement. I thought it was about 40%.

 

It is already A HV DC pulse.
What are you trying to achieve?

 

You post is confusing.
We don't know what a "diode proper placement" is.
Post a schematic of what you are talking about.