Replicas passing new emission tests

I’ve attempted a couple of sandbox replicas, but they don’t like the pollution rules. A '94 SAAB 900-like w/B234i fails WES 8 (Hetvesia in 2000); an '06 out of Focus gets the same (fails Fruinia in 92 - 14 years before it started selling IRL). Something similar to a Lexus SC300 also fails 8 (a 4 year life in Gasmea). How well are your cars doing relative to their IRL versions?
(Yes, I know I need more practice. Plus, I’ll take hints.)

It depends a bit on what they fail on. Generally, it seems like many engines wants a more rich fuel mixture than the default one nowdays, to pass NOx emissions (if you’re failing CO or HC it is only making things worse, though). Also, quality spam on exhaust/fuel might help. You have found the emissions optimizing tab too, I suppose?

(But I agree that results are strange sometimes, since a mid 80s carbed inline 4, albeit with cat, recently passed WES8 for me without even trying, I almost said Nissan CA20 clone but since it is 3V it can’t be compared)

NOx failures. All 3. Haven’t put my CA20 or RB30 in a body for testing yet. I saw the new slider an hour before I started this thread.

NOx has the opposite behaviours to the other pollutants - both in-game and IRL. The reactions that produce NOx are stronger and more active when your engine has high pressures (seen at high compression ratios) or high temperatures (tends to happen with lean fuel mixes). So, to reduce NOx, you want to reduce compression and richen your mix - but that hurts the other two tests. It’s a balancing act.

Yes, because NOx is basically the nitrogen in the air being burned during combustion.