Thanks for the feedback
Though detonation is a sound theory, a few questions come to mind.
1) None of the spark plugs showed any damage or irregular coloration. why?
2) The car is a Lonestar which has relitively quiet side pipes. I had been in the car shortly before the failure and heard no pinging.
3) other than that chunk missing, the tops of the pistons showed no signs of damage. Same with the combustion chambers.
4) the erosion I point out is away from direct combustion. You would think that if it was detonation, that the erosion would be on top near the edge.
Steve