fuel distribution and tolerances can explain cylinder-to-cylinder variance as well. Not all detonation is audible either - knock sensors will pick it up LONG before it becomes audible. I learned it the hard way with a turbo 2.2 many years ago. My top ring came out like dust, I then later cracked a chunk of the piston top out - twice. Never heard a thing until it was blowing oil out every seal and the exhaust...