Intake manifolds made of polyamide were first developed by BASF in Ludwigshafen, Germany in 1972 (with partners) and have now largely replaced metals because of optimized air flow, design freedom and general reductions in weight and cost. There have been some issues because of poor designs, but the materials have been a big success and now new plastics are being explored in response to higher under-the-hood temperatures (esp. turbocharging), demands for improved function integration, noise reduction and lower weight.
Saving weight is indeed critical to meeting the EPA mileage requirements. And the use of plastics is one way to do that. Unfortunately as noted the monkeys are working overtime. I am sure a proper plastic formulation can be found that will suit this application.
I can't wait to see how that proposed plastic engine works out. I have seen it in the news before and they are getting closer but this certainly does not bode well for the introduction of a plastic engine.
I suppose if I were charged with overseeing the weight reduction program I would enumerate all of the components and order them by weight, with the heaviest at the top of the list. Starting at the top with the heaviest items should allow for the biggest bang for the buck in terms of weight reduction.
Another approach would be to lighten the metal parts and reduce the parts count through more effective component design. I bet the metal intake manifold could be sufficiently redesigned to reduce the weight significantly but it might still cost more than the plastic manifold.
The collection of requirements that must be met represent a difficult balancing act. Cost, weight, reliability, design life, maintainability, all of these things affect the design. In this case, it would seem the monkeys tipped the balance too far and messed up the reliability and design life goals. At least it seems it was an easy fix although rather inconvenient.
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