I would recon that passing a cat test is very possible!!
The Mini just passed its emissions test with flying colours, however, it was automaticaly tested on a BET, so natural idle only which is surprising ( well it is a mini and they are notoriously bad). Results Co% 0.098, HC 155ppm that is with a shitty single point injector that dumps fuel rather than injecting it
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If dnb is geting a pass at fast idle and im getting a pass at natural idle both without a cat, then i recon its just a matter or finding the right numbers to get both on the same engine.