Engine runs on exhaust plugs only
The other 4 plugs are meant to increase fuel miles
It was an effort to get more complete combustion, 2 spark plugs per cylinder. Rarely done these days.
I really don't understand why or how they work, In 4 cilinder engines, how did they get fired? Both sparks fires at the same time?
Four runs the intake and four runs the exhaust which burns more of the fuel. On most cars the lose a lot of fuel out the exhaust.