allblowdup

I am hoping for a little help or a least a push to who I should be talking to. We ran this lsx 454 crate engine (620hp) last season and had pistons cracked in the middle, this year I have timing backed off to 26 deg, NGK tr8ix spark plugs, 100ll av gas with Lucas oil octane boost, AFR 12.2:1. Ran a total of 2 hrs at WOT (5900 rpm). Bore scoped the pistons and I got two more starting to crack same as before. Really don't have a clue but am really hoping for some help. 2 other fellow racers same motors and setup and both have cracks in pistons also.
lsx 454 crate engine(620 hp version)
11.0:1 comp
dynoed at 720 hp@6400 660tq@5100
26 deg timing
water temp 125 f
oil temp 260 f
usuage . sustaine WOT for periods of 30 min @5900 rpm

No engine mods allowed only tunig changes

mebuildit

Why are you using Av gas? That stuff is designed to work at altitude and is leaded. Is your system set up for leaded fuel? How lean was your EGT's? Did you ever try race fuel vs. Av gas?