siamesed cylinders

Siamesed cylinders are engine cylinders arranged in such a way that have no channels between them to allow water or other coolant to circulate.

The 400 differed from other small blocks in that the cylinders were siamesed and therefore required 'steam' holes in the block, head gaskets, and heads to help alleviate 'hot-spots' in the cooling system at the point above the siamesed cylinders.