Re: LM7 catastrophic failure...
I'll say at some point in your engine's life, it was beat on, over heated, or somehow stressed and this one piston decided to let go.
While the factory cast cranks in these engines are pretty good, up to about 500hp, I don't trust the stock powdered metal rods or the cast pistons. Hypereutectic cast pistons are still cast pistons, they just have a higher silicone content that old school pistons.
Unless you're building a higher power engine here, the stock crank is fine but I'd highly recommend a forged piston and rod set. A set of forged pistons start at less than $500.00 and rods start at $530.00. One of those ball honers on a drill and you'll be better off.
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1971 Monte Carlo SS454-496ci 600hp
1999 Trans Am-500hp
2003 Iszu Ascender XL Limited V8