Catalytic converters effect on MPG?

[Arragonis]

Do cats not need a certain amount of unburnt fuel in the exhaust to work properly ? And therefore a richer than otherwise needed mix ?

[fjasper]

Originally Posted by Tofuball

Creating and operating the new cat probably causes fat more pollution then the cat will ever clean up in its entire service life.

Unlikely. Here's why:
1.) catalytic converters are made from small amounts of mostly recycled materials (a few pounds of steel and minute amounts of precious metals on an inert ceramic substrate);
2.) they scrub tens of thousands of pounds of exhaust over their useful life, and;
3.) they get recycled when they're worn out. (With platinum at over $700/oz, not much of it goes into the landfill.)

Now, the question of building a whole new car vs. maintaining an old one, that's probably a different story.

I can tell you from personal experience that the respiratory impact of a single vehicle with a missing or non-functional catalytic converter can be significant. I lived not far from a platinum/palladium mine. The air quality at the edge of the mine property was never as bad as the air quality behind the old Subaru I followed on my way to work this morning.

From another site:

I like catalytic converters. They minimize the offensive odors of my car's gaseous expulsions. I wish I could put one on some people.

[taco]

I say run a pipe though the hollowed cat and weld it on place.
So there is not a wide area for the exhaust to cool to much and kill the scavenging effect. I saw a difference in sound and power when i went from. Hollowed cat to a test pipe.

Ran that set up for over 6 years. When Toyota bight back the truck last year it still had it on it.

My current daily does not have a cat either just a pipe.