The average V-shaped engine has two exhaust manifolds attached to it. One is for cylinder bank one, and the other is for cylinder bank two. The vast majority of inline engines have just one exhaust manifold. Rotary engines? They usually have just one exhaust manifold, though the turbocharged models have "down pipes" on the hot side of the turbo as well. Naturally there are exceptions to all of these rules, but in the real world, these exceptions are fairly rare. When it comes to the construction of exhaust manifolds, they are either going to be cast iron, or welded tubular steel.