Headers cause emissions changes, why?

[Jon Pike <jhpike@domain.elided>]

> You could buy some 
> "magic headers"  which would reduce your car's emissions to NOTHING, and 
> it would still be illegal to fit them to your car. That's the legal 
> answer. Now here's reality. Nobody who smogs your car is going to notice 
> (or care) that the headers aren't stock. All that is, ultimately, 
> important, is that your car still passes the smog test with the new 
> headers fitted. So, let your conscience be your guide.
Good theory..  barring you being in CA or some other "original 
equipment" state,  and your car has an
air pump,  and the headers (like just about all of them) don't have air 
ports..

I used to hear the classic Alfa cast iron headers were pretty darn good 
anyway..  you wouldn't get much
out of a new one, for street use anyway,  is this still the case?

Jon
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