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Message: [QUOTE="makaveli200369, post: 1195888, member: 16335"] Hi sorry for bringing this up from the dead but I have information to add to the thread after measuring and comparing to a 6.0 block. I took pics but it seems I have a limit of uploading 5. I feel my findings confirm what Morgan said. Its not the stud bottoming out causing the cracks but a lack of material. First thing I want to clarify is stock 6.4 bolt is threaded at least 80% the length of the bolt. Meanwhile the ARP is threaded maybe an 1.5" up. This means the stud can physically only be threaded up to the point where the threads stop which is a short distance up. For a fact the stock bolt can be threaded in until it bottoms out. Now here is where I try to find out if the ARP is bottoming out. ARP stud total length = 7.820" stock 6.4 bolt total length = 7.635" stock 6.4 bolt length to the bottom of the bolt head = 6.900" I drive both the bolt and stud in until they both stop turning and measure from the deck of the block to the end of the stud, bolt, and bottom of the bolt head. Basically how much length of the and and bolt are sticking up. ARP = 4.800" sticking out of block stock 6.4 bolt total length = 4.235" sticking out of block stock 6.4 bolt length to the bottom of the bolt head = 3.500" sticking out ARP total length 7.820" - 4.800" = 3.020" of stud is in the block. stock 6.4 total length 7.635" - 4.235" = 3.400" is in the block stock 6.4 bottom of bolt head 6.900" - 3.500" = 3.400" in the block This tells me 3.400" is the depth of the bolt hole in the block seeing how the fully threaded bolt can be screwed in until it hits. Since the stud is not fully threaded up the body its stopping where the thread ends to prevent a bottom out. (3.400" - 3.020" = 0.380") That means 0.380" of space exists between the ARP stud and the bottom of the bolt hole in the block. That is a lot of space and even when you tighten down the stud and it turns a little bit it's not going to close that gap. It would need several complete turns after the fact that it already stopped being able to turn. Okay so now that we got the bottoming out covered lets move on to material thickness. So I inspect a 6.0 block. Total length of 6.0 head bolt exceeded my caliper so I measured from bottom of head bolt to the tip = 7.675" Screwed bolt all the way down and 5.495" from deck of block to bottom of head bolt. 7.675" - 5.495" = 2.18" of bolt depth. This is where it gets interesting! The 6.0 is shallow depth compared to the 6.4 is deeper into the block. 6.0 engine = 2.18" bolt hole depth 6.4 engine = 3.400" bolt hole depth Now since the blocks are known to crack near the casting line in the lifter valley I measured from the cast line to deck of the block = 2.00" So in the 6.0 the bolt hole stops just past that line and then has nothing but meat extending past that. The 6.4 on the other hand extends past that cast line by another 1.400". So not only did the block lose meat from the diameter of the M16 increase but also from the depth of the hole. So the 6.0 has more meat around that cast line in the bolt hole area. Everyone can make their own conclusions but I thought this data would be helpful. [/QUOTE]