As stated, the mexi block is built better. Main bearing caps look like the big ones on the hipo engines. But they are not high output engines. Just a better built block. From what I can tell, they were a little nervous about the mexico castings so they added extra metal to the block in case the casting wasn't as good. the castings were good so the extra metal made them stronger. Stock US blocks can take 400 HP all the time. How much HP are you going to make? really, real HP, not the on paper it will make HP numbers. The mexi block won't make any more HP then the US block will. Let me repeat that, The mexi block won't make any more HP then the US block will. But if you are on the ragged edge of what a US block will take before it splits in half, then the mexico block is a little extra insurance without the expense of an aftermarket block.