I drive a thirteen year old +8 and my colleague a brandnew Roadster. Both produce ammonia smell under forced acceleartion. I am very much convinced it is the catalyst exclusively. My theory is (being a researcher in chemistry) that under hard acceleration a rather high amount of hydrocarbons are not burned to CO and CO2 and reach the catalyst surface which is composed from noble metal particles supported on rather ordinary metal oxides (iron oxide among them). The latter are actually catalysts (or precursors to them) for the conversion of nitrogen to ammonia (the industrial Haber-Bosch process for ammonia production relies on reacting nitrogen from the air with hydrogen produced from coal and water). It may very well be that this process is operative under excess conditions of hydrocarbons (fuel). There is not much one can do about it and it will not do any harm to the car. Best thing: Slow down and behave properly in civilzed aereas and accelerate in the country side where a little extra ammonia will not be noticed. I would keep the catalytic converters....
