> My experience comes from driving and working on a 1988 GMC 6000 truck with an anemic 350 small block with a Muncie SM465 behind it. There was no catalytic converter,

Catalytic converters were required on most vehicles starting in 1975 in the US and the requirement was expanded to cover all vehicles in the early 80s.

Your truck was modified by someone.

Medium duties are weird beasts indeed.

Well, FWIW the air pumps still can -help- with unburnt fuel...

It's not as good as a Cat for emissions but it's better than nothing, so they actually started being used before Cats; they just are used different now.

In 1988 the factory put a cat in the exhaust. It also would have had fuel injection and a computer, and thus no choke. In short this truck was very much not stock (or possibly you are not in the US?) and so it is interesting but not helpful for the discussion.

350ish (or less) + 4spd trucks kinda fell out of favor over the course of the 70s for bigger engines and 5spds (usually with a 2spd rear end but I digress). I'm sure you could still get one, but who would when you could get something better on the lot for the same money.

Sounds like someone swapped a 70s-80s engine from a lighter application in.

I don't think that truck would've had manual choke from the factory. Lots of stuff could've happened over the years.

The amount of air your engine breathes is monumental compared to what the smog pump moves. The math of dilution just doesn't work. What does work is pissing a light stream of oxygen (remember, not much of that coming out of the engine, especially on warm up while it runs rich) to help the catalyst burn those hydrocarbons off of itself a wee bit faster.

I'm not sure if an 80s gas MDT would've had cats from the factory.