I built a high energy system with a follow-on energy supplied by a capacitor. The capacitor discharged to prolong the spark, no initial delay. The plug made very loud pops and bright light. The follow-on supply that charged the capacitor to 300V could be switched off to test, with and without. The test car was a VW Beetle air-cooled engine. The stronger spark, resulted in a better idle during warm-up. The negative - plug wear was very significant!
I went on to build an Engine management system and used waste fire for simplicity.
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