Quote:
Originally Posted by 10"
The official reason was emissions standards changing. The Z4 continued with the N54 but it's very low volume even compared with the 135 and 335. The N55 was a much cheaper engine to make. No forged internals, single turbo, and really good performance. That being said it was no N54. The S55 was largely built in the basis of the N54 idea.
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The N55 was undoubtedly simpler and cheaper to make, but it’s really only the N54’s forged crank that is an advantage, assuming stock power levels, and even the advantage of that is dubious at stock’ish power, since failure is unlikely to happen. Both had forged pistons, and the N55 has better cooling channels in the block, valvetronic, is smoother, has a larger powerband, sounds better, is more environmentally friendly, and is generally more reliable, among other things.
Of course, all of that goes out the window if you’re going for big gains, since you’d want those twin-turbos, but, for anyone not going for 450hp+, I’d pick the N55.