Hi Peter, I was just about to respond that the Co2 after the cat was more than before the cat. So this proves new cars are producing more Co2. But after reading your post again I assume you mean that less C02 is produced during the manufacturing process of the car itself.
On your second point, I quite like oxygen to, I was just pointing out out how it was consumed in the cat during the process of cleaning up Co and Hc.
Sorry I worked out what BTW and HTH mean but I don't know what VBG stands for, could you enlighten me? Perhaps we need a glossary for these abbreviations or am i the only one getting confused? I'm sure I will feel silly when you tell me.