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It might be that the cars with the secondary cats are SULE cars (ie CA specs). ?
The three stage intake manifold is also called: DISA. IF you google that you will find lots of info about how it works. BMW has used that DISA intake manifold on lots of other models as well. Some of the German tuners can reprogram the two stage intake (DISA too) to make a big Hp increase. Normally they can get around 275 PS with just a chip tune on a N52.
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