Originally Posted by MTPZ06

Sure...there can be more than one way to grenade an LS7; but my take aways... Its a "one owner" 2007. I can only surmise this as being a bone stock car, but OP please correct me if I'm wrong here. I see in the first photo the cylinder head is missing the exhaust valve head. Its somewhat of an understanding that earlier model years had a higher propensity to snap an exhaust valve. Around May of 2008, GM had a part number change for the C6Z exhaust valve, due to a change in suppliers. Many of us feel the change in suppliers was due to QC issues with the previous supplier's manufacturing. I'd have to dig a bit more for the exact numbers, but the newer OEM exhaust valve had thicker (more consistent) walls...bumping up to something like a wall thickness of .041"

Early ('06-'08) valve inconsistencies in wall thickness, as well as variances in the amount of sodium fill were discovered:



These inconsistencies in wall thickness, coupled with the non-concentric guide to seat machining courtesy of Linimar would over time lead to stressing the valve in a manner such as this...



Exhaust valve discoloration (different from others) due to inadequately amounts of sodium fill:



There's a ton of old/archival information here that can be sifted through, but at the end of the day...I personally feel this was a good old fashioned exhaust valve failure.

Again OP, if your boss's car is highly modified, tuned, etc., the cause of the failure may be different than I described. Crap tunes by inexperienced "tooners" usually result in a lean condition that will more often than not crack the "#7 cylinder liner". Do you know which cylinder failed on the car?