No, there's no difference at all. A petrol-engined car with an open-loop-controlled cat is also classified in the Euro 1 pollutant class and doesn't qualify for any colour emissions sticker (Germany-specific). The only way to gain in any respect is to retrofit a closed-loop cat, i.e. a KAT 2000 system from HJS.
Last update on 2013-07-05 by Stefen Baetge.