The wear pattern is consistent with detonation wear caused by running too much boost for the state of tune combined with the octane of fuel being used. The center cyl's always see the most heat because the outside cyl's transfer heat to the center cyl's as well as the heat made by the center cyl's. When a cyl runs hotter it detonates easier. Every Z I have ever seen that has had rod bearing failure from detonation (With or without a Pulley) has failed on one or both of the center cyl's. The only reason pistons #5 and #6 melt first is because the thickness of the #5 and #6 cly wall to water jacket is thinner. The only reason VG30 engines have rod bearing failure is because too many people think they can run crazy boost levels on pump fuel. I have never seen a VG30 turbo motor have rod bearing failure or have premature bearing wear while running reasonable boost levels for the octane of the fuel being used with or without a harmonic balancer.
