Originally Posted by ScOoTeR
Not true - many cars have air pumps on them even now!
The big difference is that they are electric and only run for the first 20 seconds or so after startup. Back then, it used to be about reducing emissions from poor fuel control with shitty technology cats -
NOW, it is all about getting the super-efficient cats up to operating temperature as fast as possible. One car I'm do some work on gets center catalyst temperature to 700C IN 20 SECONDS. The sooner you are hot, the quicker you reach your best catalyst efficiency.
I had to google it after reading your previous posts and found the wikipedia article on it. Interesting. I swear I read in some old school car mag about smog pumps just pumping air to thin out exhaust and make a false tail pipe reading on the sniffer. I guess you can't believe everything you read and magazines are not gospel. Your explanation which is exactly what wiki said makes a lot more sense.