[Kurt S]

2 relevant posts from John Z from the CRG site:

Factory smog calibration in those days was simpler on automatics due to the relatively constant and progressive engine load conditions; with a manual, engine loads (and carb metering variations) varied widely, and A.I.R. was required to overcome the rich mixture "spikes" during acceleration and manual gear-changing. Same issue at idle - automatic cars were under an even, constant engine load, but manual cars weren't - that's why A.I.R. cars had retarded base timing, ported spark, and later advance curves - created a rich idle condition, which ensured there was enough unburned fuel in the exhaust gases at idle to "keep the afterburner lit" in the exhaust manifolds with the injected air to keep tailpipe HC numbers down at idle (this also created more heat and higher coolant temperatures at idle). That rich idle condition is why Gary had such a battle trying to pass the HC portion of the Delaware emissions test without the A.I.R. system in place and operating to burn off the excess hydrocarbons in the exhaust manifolds. Later on, catalytic converters simplified calibration somewhat, and even later computer-controlled closed-loop port fuel injection systems coupled with catalytic converters solved it entirely (at VERY high cost).

(The above) post applied to the SB issue; the big-block Camaros were a separate issue, and Jerry is quite correct that ALL big-block '69 Camaros (L34/35/78/89) had A.I.R. systems, regardless of transmission application. EPA emission certification was done not only by powertrain, but by carline application, vehicle weight, aero drag, and coast-down horsepower testing, which created many variables. Every different situation required full EPA certification, including 50,000-mile durability testing, and Chevrolet apparently decided that rather than go to the time and expense of developing and certifying eight different low-volume Camaro big-block combinations, they'd go with only four, that they knew would pass and certify with A.I.R. For the high-volume passenger cars, however (Impala/Caprice), which were built in Nine assembly plants at 7,500 per day (vs. only one plant of Camaros when you factor out the Firebirds at Norwood), it made sense to certify high-volume passenger car combinations as much as possible without the added per-unit cost of the A.I.R. system, so many full-size Impala/Caprice big-block applications were developed and certified WITHOUT the A.I.R. system. I had a brand-new '69 Caprice 2-door hardtop with the 427/THM400 combination, and it didn't have A.I.R. either. Full-size cars and Camaros were totally different certification situations.