Originally Posted by Cozy
Is the 335is N54?
If so I can't see why sticking N55 335i mids on would be an issue, they must follow the same path.
The N55 is a more fuel efficient engine with one large cat in the downpipe. The N54 is fairly polluting and as a consequence has four mid-sized cats to controll its emmissions.
Yeah the 335is has an n54. And that's interesting that the n54 pollutes the air so much more as it is really only about a 5 to 6 year old engine. However i guess technology changes quite rapidly these days.