Originally Posted by chaFT328i
Someone correct me if I'm wrong, but isn't it that 328s in California uses the SULEV engine(AKA N51) which has a 3 stage due to different emissions?? IIRC, only difference is that the 328s are detuned so the 3 stage isn't at its full potential, and that a tune would solve this.
Yes, the N51 does have the 3 stage intake manifold. However it also has a lower compression ratio than an N52 due to a redesigned combustion chamber (10.0 vs 10.5 I think). I think the 3-stage intake was meant to help make up for that or maybe it has some benefit for emissions.
I have an N51 with an AA tune and modified exhaust. I can tell you that it's plenty fun to drive and not at all short on power.