Does anyone know what goes in this spot on the firewall?

MoparMike1974 said

Im aware, just not knowledgeable on the details. What impact could exhaust tips have on emissions?

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Apparently they decided to impose restrictions on noise emissions as well as exhaust & evaporative emissions..

The no tips rule only applied to 426 Hemi & 440-6 cars and even with them there were some cars that snuck through with tips...