360 Bore

"If I Remember Correctly"...lol. I recall reading that for a bunch of engines that were used thru the 70s. I recall where but I think it was a rebuilder's guide the machine shops have/had. In any event, Jim while very bright, is generalizing. They were cast with a better iron, but the castings were made thinner. But it had nothing to do with the reality of Mopar castings... They suck. As most manufacturers' were at the time. They suffer from core shift.. which means when the cores were first set for the block molds, the sand cores were not placed perfectly and the result is bore centers that were off in any direction of the compass. Every cylinder has two thick directions and two thinner ones. They should be oval if you cut the decks off and looked straight down. but if you dont have the mold centered in the spot, one thin side gets really thin, or one thick side gets thinner, etc. That is core shift and every block I've ever tested except one had it to some degree. (In case you're wondering, I do own a really good sonci tester and know how to use it) So you want certain minimum thicknesses for strength and for heat dissipation. The factory stated small oversizes because the really bad blocks get really thin at larger overbores. I've had to sleeve two blocks because one or more cylinders were too thin to run the power level my customer needed. The other holes were fine, but one or two int he 8 were badly shifted and that left the thin side on one at .080" before boring, and the thick side (called the major thrust of the cylinder) was around .120" thick. So by cutting it out a sleeve was isntalled to correct the bore center and we were good to go. I am leary about buying any .060 over block. I will bore them to there after testing, but buying a fresh one thats .060 over isnt a big deal. Buying a running engine at .060 over and partially thru it's service life leaves no room for rebuilding. While not often, I have done 2 +060 4" arm small blocks that are fine. (both of them required sleeves to get all 8 thick enough) For a stock stroke, 060 over isnt a big deal but I'd want it all brand new at .060 over. Not used or bare at .060 already.