When two turbos were no longer enough, BMW applied three. The outcome – a 2,993cc straight-six diesel with three turbochargers supplying 4bar of boost. The engine generates 740Nm from 2,000rpm, revs to 5,400rpm and, in the M550d, emits only 165g/km of carbon dioxide. The system comprises two small variable geometry (VGT) turbos and a large fixed geometry turbo.
[Source: Automotive Engineering, June 2012]
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