[i] The 4-bolt 400's are crack prone, but the 2-bolts are not. Most claim the overheating issues have to do with the 400's siamesed bores, the bores actually touch between cylinders in the water jacket and there is no coolant flow between. I don't necessarily believe this to be true. Most racing engines use siamesed bores. GM's new LS2 and LS7 engines both use siamesed bores. I believe the overheating issues to be caused by the fact that a 400 is a big block in a small block package and retains the small block cooling system. Just make sure your cooling system is sufficient and you'll be set. [/B]

I have both 400 2-bolts and 4- bolts sitting on the flooor of my shop with 3-4 inch cracks in them.Some in the lifter valley and some between the freeze plugs.Of the 400 2-bolts the 817 blocks are the strongest.I have weighed both the 509 bare 2-bolt and the 817 bare 2-bolt blocks.On the ones I weighed the 817 block weighed 11 lbs. more.Was it just those blocks?I don't know but the 817 did look like there was more metal in the main web area.