91 octane gas. I was putting in octane booster but replaced plugs and stopped using the booster for about 4 tanks of fuel.
Bkre611 ngk plugs. 10:1 compression. It's a 415 dual quad indy cylinder head engine.That’s the red you are seeing on the plugs.
What’s your compression ratio and what spark plugs?
Only took out 2,4,6,8 plugs.Any other plugs look like the 3rd pic ?