Re: Why do so many people fail air cleaner class?
In my youth, the thing to do was put on "Polish Headers" by flipping the air filter lid. It would still seal on the filter, but leave it open all the way around, and dip down in the middle. Like a free "warm air intake". Probably lost power, especially on hot days, but sounded cooler!
Then your dad could tell because it would make an imprint on the hood insulation, fun times.
My experience with that was on a 1975 Impala with 350 2bbl.
1967 El Camino Malibu - Deepwater Blue
ZZ4 350, FiTech 600 complete!,Roadmaster tank, 700R4, Underdash A/C in progress, JGC Steering, 1990s truck serpentine.