Abstract: A composite engine block for an internal combustion engine having a fluid cooling jacket, comprising a bipartite liner structure with metal (i.e., aluminum alloy or cast iron) defining at least the combustion zone walls, the structure having one or more open cylinders of a first part mateable with a corresponding cylinder head of a second part, the first part having (i) an integral base plate extending transversely outwardly from the cylinder to define a lower imperforate membrane for the bottom of the cooling fluid jacket, and (ii) walls extending dependently from the base plate to support a crankshaft for rotation about an axis transverse to the cylinder, the second part having an integral top plate extending transversely outwardly over the cylinder head to define an upper imperforate membrane for the top of the cooling fluid jacket; (b) a tri-partite skin structure comprised of nonmetallic light weight, vibration damping material (i.e.