Quote:
Originally Posted by The HACK
EDIT: I don't think high compression ratio is the primary contributor to bearing issues, especially considering all these engines are equipped with knock sensors to retard timing to prevent detonation. And in BMW engines the S54's compression ratio is middle of the road. The M57, for example, has a compression ratio as high as 18:1. Spun bearings has not been an issue on the M57. High compression combined with stratospheric top end RPM? Maybe.
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Not sure comparing a direct injection diesel engine to a manifold injected gas engine is an apples to apples comparison, but I agree RPM limit is more a contributor. Back in the 70's if you wanted to high rev a big block and keep the bottom end inside the block the standard practice was to change the rod bearings every other oil change. High rpms and rod bearing wear/failure isn't a new issue invented by BMW. Oil has a compressive limit and at a given force level struggles to keep the spacing between the rod bearings and the crank journal.