For you non racers, look at the piston pics post #35, that is known as "BLACK DEATH." It is caused by insufficient piston to wall clearance, I.E: not enough clearance in the hone, due to the machinist not knowing what alloy the pistons are,(always provide pistons and data sheet to machine shop,) machineshop doesn't have turbo experience so he doesn't know how much clearance to make, machinist believed the guy you bought the car from when he said:" set it up tight, it's just a driver/ show car, and I don't like a noisy engine, I'll never turn the boost up."
Or YOU: leaned it out, (many causes),
Ran the " summer tune when it got cold out."
BLACK DEATH usually looks worse than it is, the pistons bear the brunt of the destruction, the walls often clean up at .005", don' get too excited until you get an exploratory hone done on the worst cylinder.
This piston is out of my 572, 14-71 blown, intercooled, boat. I probably should have switched to the other full tank before running about 15 MILES WFO on Havasu.....
BUT, the bore actually cleaned up at .008" over!
I would do an exploratory cleanup hone on yours.