the building flux field is so quick that secondary output exceeds the  voltage required to jump the air gap and flow along the lead salts, and arc out  of the back end of the spark plug boot to your Twistoflex watch band, and  lay you out on the hanger floor.................All on the way up to peak  current  The MSD (and other) systems use about one amp per thousand RPM. You don't  want any part of that kind of energy.
 
Picture is from Western Electric when I still had a mind.
 
Lynn E. Hanover