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This is put in this section because my theory is one of our bolt-ons caused this (specifically, a lean condition brought on by the FAST EFI at high RPM), but I'm open minded.
I've heard a few theories from folks who are "sorta knowledgable"about engines, but wanted to put this out to a more general audience. Maybe we can all learn something, like avoiding this issue in the future.
The engine is (was) a LS2 shortblock from a 05 GTO, with AI ported 241 heads and custom cam (600 lift, 234 duration, 110 LSA). It ran VERY strong. It had a carb style intake, long tube headers, a FAST EZ-EFI 2.0 coupled to a MSD 6010
Background of incident: the car was being driving at Road America, and performing relatively well. We'd noticed it had some blowby and crankcase pressurization early in the day and the car only made a couple laps each in sessions 1 and 2. The car had done a track weekend at Gingerman three weeks prior, and had no issues to speak of. Solid oil pressure. No stumbling or odd noises. At Gingerman, it pretty much ran the whole track in 3rd gear, with occasional upshifts into 4th.
We though it was a oil leaking and pcv issue, fixed it as well as we could and sent the car out on session 4. It came back early again with a what sounded like a rod knock. We bundled the car up and ended the track weekend early. I pulled the engine last month and opened it, and this is what I found. The block looks fine and nothing in the bottom end looks or feels loose (bearing slop, etc). The combustion chambers are a bit banged up, but the heads are fixable.
well it looks like the valves were contacting at least a couple pistons judging by the marks there, are the valves ok? its odd because it didnt just happen to one cylinder.... what was the afr on the car at wot? could it have been lean?
EDIT: I just reread your post and I agree with your theory looks like it might have been lean and let go.
Judging by the burn pattern on the pistons, it doesn't really look lean. Obviously you lifted the ring lands, which just could have been because of the heat that a road race engine sees.
the block looks fine, and I'd potentially venture to say the rods may be ok too (have my doubts after piston bits got smashed between the head and rest of the piston). The bores on the block look beautiful still.
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Piston carnage - what would cause this? 
