Fig. 42.9
When picking a block to build and especially when you are going to be boring it you should look for core shift. The best way I have found to check core shift with out having the block sonic tested is by looking at the boss around the front cam bearing bore. The boss should be the same thickness all the way around. Looking at arrows "A" and "B" in Fig. 42.9 you can see a difference in the thickness of the boss, this is a good indication that this block has some core shift which for most small-blocks 0.040-inch over size is the maximum it should be bored with out sonic testing. The minimum cylinder wall thickness on the thrust side of the cylinder wall for street use is 0.130-inch and for high output race engines 0.200-inch is minimum.