block dart chevy sb 434, carburetor holley progressive 950, cam LS:110 dur @.050 int: 248 exh:254 ratio compression 12.9:1, 350 shot Nos fogger using progressive, runner intake 221cc runner exh 75cc, fuel used c-12, timing beginning 40° without nos then a retard of 14° as nos is applying, the retard was 10° first gear, 4° retard at second gear, transmission powerglide, sea level 1540 meters

a piston got a hole
what went wrong?