Dave, Joe, and Jeff,
I agree that of all the cool and unknown options, this has to be one of the neatest. I never saw or heard one of these cars back then and Dad never mentioned them either. He grew up with musclecars during this time and we went to the dealership every new year's introduction to see Pontiac's hottest. (Remember when people did that??) I would have remembered this option. To be able to bring back the OEM sound on the few remaining GTO's is a lot of fun.
We have made some changes internally to help smooth the air's flowpath while keeping the sound differential they need. This way, they can be used on street rods and other muscle cars, like my 340 Barracuda, and not restrict the airflow too much
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Tom