Originally Posted by AW128i
According to the EPA's website, there are actually three versions of the 128i engine in the U.S.: Bin 5 N52 (Federal), ULEV II N52 (CARB), SULEV II N51 (CARB). This spans the entire E82 U.S. production (i.e., 2008-present). I'm guessing the CARB version of the N52 has the secondary cats and the Federal version does not.
I have now verified that I have an N52 by punching my VIN into Real Oem. I still am interested in learning if I have a three stage intake.