US-spec 1974 911s shipped without smog gear or thermal reactors, making them mechanically simpler than the 1975-1977 cars. This is repeatedly cited as a reason to seek out 1974 pre-SC Carreras specifically, and is the underpinning of the 'pre-SC will climb first' market thesis.
1974 was the only G-series year without smog equipment or thermal reactors
Porsche 911 (G-series) · factory-spec