In My Honest Opinion -- (I, MHo)

OpenIdea: Lightweight engines made of plastic?

I wonder if more efficient hybrid vehicles could use engines made of plastic? hmm. If the engines are used only as generators, then they might not need to be made out of metal (which can be heavy and expensive).  It might also make the engine more recyclable?  I assume there must be a reason why engines aren’t made of plastic, though — perhaps no plastic is strong enough to withstand the stresses in an engine?  But if an engine is used only for generating electricity, you’d think that the stresses could be minimized since the plastic engine is being used to directly haul the vehicle….  Maybe instead of a pnematic-ICE hybrid — an electric motor with a type of low-pressure ICE pneumatic generator is possible?