That's a 109 casting out of an '86 or '87 Buick Grand National or T-type. Takes waaaaaay more than 24#'s to make them act up, but damn. That's some serious splittage. I can't imagine the amount of detonation to make that happen (and how bad ass the pistons are to let it get that far). Normally the 4bolt head sealing won't let it get to that level.
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