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      06-27-2011, 12:13 PM   #3
AW128i
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Drives: E82 N51
Join Date: Nov 2010
Location: Southeastern, PA

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My car is N51-equipped and it has the secondary cats under the car. It also has the 3-stage intake manifold, secondary air injection, and an ozone-fighting radiator coating, all of which help it achieve the SULEV II EPA rating. I can't verify the reduced compression ratio, but it's heavily rumored that the N51 does have a lower compression ratio than the comparable N52. I can tell you from personal experience piloting both engines that the N51 has a slightly but noticeably different power curve than a comparable N52.