slantsixdan said

The "silver" resonator is aluminised. The "black" one is zinc-coated (galvanised). Mufflers were available in both varieties through Mopar for most applications right from the start; as particular applications grew older and demand dropped, often the more expensive aluminised unit would be dropped and only the cheaper galvanised option would remain (or mufflers previously available only as aluminised would be downgraded to galvanised) to compete with the non-Mopar aftermarket muffler offerings on price.

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