BMW made E21 and E30 323i's that were the fastest of the 3-Series of their respective times. No M-versions were made here or there. I had an E21 323i with base hp of 143 and later replaced the block with that from a 3.3L. They did make an M320i that was the earlier hot E30 I-4 and it was the immediate predecessor to the E30 M3.