5 zigen and Tora, your comments are appreciated.
Tora, you are correct that the 'popular belief' phrase is debatable as I have no study to verify what people think cats are for. But here on the forum I have seen people suggest that that by removing your cat you are contributing to global warming.
Catalytic converters are nothing more than complex incinerators that use a three-way catalyst process to superheat unburned fuel as it travels through the car’s exhaust system. As a consequence there is increased green house gas emissions (GHG) in the form of carbon dioxide and nitrous oxide being expelled.
My statement about the noise of a catalytic converter is true. If I am running a catless downpipe and a stock cat back it hardly makes any more noise than stock. Certainly way less than an aftermarket cat back would make. The muffler and resonator dictate noise levels way more than a cat or lack thereof.
Regarding odour, yes you will smell more unburnt fuel behind my car if it is catless, but is it more toxic or potentially dangerous to breathe? Absolutely not.
Also the production and transportation of catalytic conveters themselves uses considerable fossil fuels and directly creates even more Greenhouse gasses. It's just true.
I know that the stuff I'm saying goes against even what I thought about catalytic converters before doing some research so I expected some debate. As long as it's done in a respectful way, it's actually constructive. But guys, don't try to pull out the 'young kid doesn't know any better' card because it just makes you look old and ignorant.