With all this chatter regarding O2 sensors it is apparent that many do not
understand why they are really there and why such tight mixture control is
needed.

The 3 way catalytic converter has to actually support oxidizing (lean
mixture) reactions to reduce carbon monoxide and unburned hydrocarbons and
reduction (rich) reactions to reduce oxides of nitrogen, (NOx). That is why
"crossover" of the mixture is so important. The goal is not to maintain a
set mixture, but to run rich and lean to keep both sets of reactions going.
NOx reduction is extremely important and the reason we had the dynamometer
tests in many areas. The Vanagon engine relies on the combination of low
compression, piston design, conservative ignition timing, etc. along with
the cat to achieve the NOx goals. It is further hampered as it does not use
any exhaust gas recirculation, (EGR). For the CO and HC it also does not
have the benefit of air injection reaction in the exhaust. Proper combustion
and cat is all it has.

It is a bit counter intuitive but increased performance or efficiency does
not always equal lower emissions. NOx is a leading contributor to air
pollution and its effects on health can be very nasty. For most combustion
processes there is a trade-off between efficiency and the production of NOx.
This was the major reason that Diesel became a bad word for many years here.
Here in NY your couldn't buy a diesel car from 2002 to 2006. 2007 bought a
better round of emission controls including the lower sulfur fuels so
Diesels too now have catalytic converters. Just like recycling and other
"Green" initiatives cleaner air does cost more. This fight goes on for
boilers and power plants etc.

Dennis