Originally Posted by AW128i
The N52 with the secondary cats is ULEV II-compliant. The N51 has lower compression, 3-stage intake manifold, secondary cats, and ozone-reducing radiator and is SULEV II-compliant. The N52 without the secondary cats is Bin 5-compliant (i.e., LEV II) and is only available outside CARB-compliant states, but I'm not sure if maybe some of those states offer the ULEV II N52 by choice/default, or how exactly it works.
Also.... I think all Military Car Sales (MCS) orders get the ULEV cars - incase a service memebr is from one of those states that require ULEV spec/cars.