I'd be curious how this pans out long term too and what the A/F ratio is running at. Essentially all the cats do is take out the peaks and valleys of what's left over after combustion, for it not to throw a code it has to be running at nearly 100% efficiency and E30 is still mostly gasoline. On the base tune it's managed to not only skirt the non catted system, but do it without setting lean pre cat codes. Pretty interesting to say the least. Is it a function of the lambda style sensor?