Great article from 2008 was just posted.

Catalytic Converter Face-Off | Articles |

 

Interesting, it seems to basically only affect CO and idle HC.

Thinking back, I think my old honda didn't actually have a working cat. Its hydrocarbons only dropped to something semi-normal around 1100 rpms. I got through smog in CA by fiddling with my idle to find a window where the RPM and HC were both barely legal.

 

I wish they would have measured backpressure with the different cats.

Also, that kind of emission test underrepresents changes in emissions because the engine is warmed up.

 

I was kinda hoping to see videos of somebody shooting holes in catalytic converters