[Commander]

because of GM's design, the 400 with siamesed cylinders had cooling issues. Steam pockets were created under the deck because there was no flow around the cylinders at that point.

supposedly, that is not an issue with the Genesis blocks.

everyone is implying that siamesed cylinders can be bored to the extreme of a .10 wall shared by two cylinders. Not so.

a siamesed cylinder works better generally because it is thicker overall, stiffer, less prone to distortion.

it IS connected to the next cylinder(s) along a line though. Heat these cylinders up, and constrained as they are by their neighboring cylinders, you'll get out-of-round distortion. bore these connected cylinders and you'll experience MORE of this out-of-round distortion than you would if the cylinders were free 360* around. So siamese cylinders CAN be good, just don't take all that metal as a free pass to bore the daylights out of them or you'll have ring seating (and other) problems like you wouldn't believe.