[mgarblik]

Detonation is not impossible, even on alcohol. Just for kicks, check the ring side clearance very carefully on the top ring land all the way around. If the gap is opening up, there is mild to moderate detonation going on. Can't say if it would cause that crack though. That's a bit of a puzzler. Certainly have the crankshaft checked for cracks. I have seen many cracked shafts ruin a block. Sorry to hear about this happening, but you caught it in time to save many valuable parts for re-use. As a side note, I would strongly recommend using studs in the outboard cap holes when you put your new engine together. Studs can go 3/8"-1/2" deeper into the block than the cap screws you have in there.