Dates and availability of chambered exhaust option

[bergy]

This is probably a topic that has been discussed many times, but does anyone have the definitive answer to when GM officially stopped installing chambered exhaust on 1969 Camaros built for US sale? I have an 05C bb pace car that has documented chambered exhaust from the factory, but it is an export (Canadian) car. It is my understanding that Chevrolet stopped installing US Camaro chambered in early 1969 - after prompting from DOT. Can anyone add insight or direct me to a previous thread on the subject? Thanks, Bruce