Yeah I know what you mean about getting behind a 60's V-8 engine
car.  You smell all kinds of stuff.  To me it mostly smells like
unburned or partially combusted gas and oily blowby gasses.  Kind
of  amazing how there is basically no odor at all with the modern car engine.

I remember seeing in service stations the posters about it being a
federal crime to remove or disable emissions equipment with $25k
fine.  And being threatened about that for something on one of my
cars over the years.

I believe that in general European emissions laws are more about
reducing total greenhouse gasses vs US wanting very low NOx, among
other differences.  That's why they have incentivized diesels and
it's hard to get many of their very nice diesel engine cars to be
accepted by US regulators.

Edward