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Originally Posted by epiphone3
The only reason the S63 was lighter than the S54...
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I think you must have mean S65 there, yeah? I am pretty sure that the S63 is a lot heavier than an S54 (and by extension, S65) due to all the turbo infrastructure.
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...the S54 used an iron block to have strong enough mains to take the 8,000 rpm rev-limit with such a long crank.
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My understanding was that it is the fact that the bigger bore means less space between the cylinders and an aluminum block was not strong enough to take the massive heat and side wall forces. The mains might have been an issue too, but man, there are some pretty stout motors out there with aluminum blocks and the mains don't seem to an issue. Whatever their reasons for going with the iron block, sure, the lower RPM of the turbo motor might mitigate all of it somewhat. But in the end you are still a slave to the 91mm bore center of the modern BMW I6 engine architecture. So, if you go with the 87mm bore of the S54, you only have 4mm of material between the cylinders. That's really tight. I don't know if aluminum will cut it in that application, but maybe with modern advances they can build an aluminum block to those specs that will meet reliability and longevity requirements.
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Therefore, 440hp with a lighter engine is possible in my opinion. This would align with the strategy and leave M something cool to do.
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I still think they can get 450hp+ with 3L, since there have been 2L I4 engines with 300hp+. Though currently, I believe the most powerful 2L turbocharged motor in the US is 291hp in the Mitsubishi Evo, I am fairly sure there are or were 320hp+ versions elsewhere (400hp if you include the ultra-limited FQ400 in the UK).
Quote:
Originally Posted by phlfly
Why do BMW just take S54 make direct inject and twin turbo.
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See above. The iron block is one big disadvantage of that solution.