Thoughts about CO2, CATs, & gasoline fuel economy
 

If burning one gallon of gasoline produces 20 pounds of CO2 (is that true?), and if a car with a properly functioning CAT is modded to get 60 MPG instead of 30 MPG, hasn't it halved its total CO2 output?

AND

If gasoline catalytic converters produce CO2 from the CO and hydrocarbons in the exhaust, then isn't it possible that a 60 MPG car modded to run WITHOUT a CAT emits less CO2 than a 30 MPG car with a perfectly-operating CAT?

(Obviously, emitting poisonous gasses such as CO is not a good alternative to emitting CO2, but I am curious what you all think.)

I don't follow the 2nd half. Any 60 MPG car regardless of cat will emit less CO2 than any 30 MPG car, regardless of cat.

The first conclusion is right though. Burn half the fuel, emit half the CO2. Again, that's basically true regardless of cat status.

But the comparison in the second question is between a car with a catalytic converter and one without a catalytic converter. So, if one of the cars doesn't have a catalytic converter at all, does it still emit any carbon dioxide and how much? Phrased differently, how much carbon dioxide is emitted by a car without a catalytic converter?

I don't think catalytic converters effect car fuel economy at all or barely at all.
After driving my electric so much I think fuel burners all stink. If you want to reduce back pressure removing the muffler and running just a converter would be better.

I'd have to do the research (google) because I don't know the proportion of CO2 vs CO with/without a cat.

That said, my hunch is that the difference is negligible, and it would be better to produce CO2 than CO, even if it's a stronger greenhouse gas.

The main byproduct of combustion is water, though.

I don't know it either, and a few searches took me down CAT marketing pathways and old science justifying CATs, or else descriptions of how commercial CATs operate. What I failed to find was info answering my questions. To be clear, I am not interested in deleting my CAT. I am actually interested in adding one instead of a muffler. I want my car to puff pure CO2 and O2 when it runs... and I daydream about all wheel drive via rear electric hub motoers integrated with the throttle and gear shifter somehow (I lack the knowledge and experience). A parallel DIY hybrid... in EV mode it would be "greenest." ...

By number of molecules, but not by mass--one gallon of gas produces about 16 pounds of water but 20 pounds of carbon dioxide.

And N2, the other molecule emitted by catalytic converters.

CO is oxidized in the atmosphere, so the CO from a car's tailpipe eventually still becomes CO2. It just takes longer.

CO will become CO2 in time and when it does it will make O3.

O3 has a short halflife in the order of hours to a couple of days depending on conditions.

It either oxidises something or decomposes in to O2.

O3 is classified as a secondary pollutant.

if you have an older car install a newer 3way catalytic converter.

you can get good aftermarket highly rated 3 way converts pretty cheaply (get a California CARB rated 3way converter, don't get a 49state one as those are poorly made)

(1.6liter)
82444 walker cat would upgrade you to
2001-2005 standard