And, of course, there's always the hope that new materials can make engines less costly to manufacture, usually by virtue of parts reduction through integration. Below, you'll find Bahavsar's analysis of engine materials. This would have cost advantages over traditional cast and machined aluminum or steel. However, there are still a few issues to be worked out before all of these parts get incorporated into a composite intake manifold. First, as Bahavsar explains, steel advocates have made great strides in improving manufacturing methods to cut cost and weight.
Steel also holds an edge when it comes to recyclability.
Furthermore, an integrated composite fuel rail might have a problem with emissions. Since all plastics are permeable to some extent, the potential for fuel evaporation through a composite fuel rail exists. Regulators who are concerned with the emissions of a single drop of gas spilled outside of a fuel tank will not be happy about this. Another rub on plastic is that while most engineers are fairly adept at designing aluminum manifolds, plastics can give them headaches. Plastics have a low modulus, which causes them to transmit much more noise from the engine.