[atmosphericM]

I see no reason why the BPC tune wouldn't do *almost* just as much for a SULEV 328i (N51 w/ 3IM) as it does for a 330i (N52 w/ 3IM) or a standard ULEV 328i with the 3IM upgrade (N52 + 3IM). The slightly lower compression ratio probably robs the tuned N51 of about 5 maybe 10 whp max, based upon my rough calculations, when compared to a tuned N52 with the same mods (3IM, intake, MILVS, headers, exhaust, etc.).

That said, only those at BPC really know what the difference in their N51 vs. N52 tunes are.