Exhaust valves open approx 180° after combustion start so in your example 1)180 2)420 3)660
For your info its the opening of the exaustvalve that gives the poef noise in the exaustmufflers not the combustion itself.
I think the 2sparkplugs give a fast, equal, complete burn as is.
Adding a 3th will not be necesery or usefull in a exotic 800hp tune. lol
Kind regards
Vic
