That was actually exhaust side.... Just flat out leaned out....
Ironically; that cylinder came out nearly dry; compared to the other 3 wet.... And this is like a year after it happened. He finally got a bug to fix it.
It was a jdm d15; eagle rods; double head gasket to clear pistons; 1mm over; ramhorn; hy35; full headwork/cams/springs/retainers.... Went silly with tolerances, bearings, and clearances.
Damned boost cut was set; at 1.5psi below the set point the map sensor topped out (early) thus boost kept building and no fuel being added.
I think a failing injector may play a part considering how the one melted cylinder was dry compared to the other 3 that were oily/shiny still.
It was a sad day; it was pretty damned quick.