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Automotive Engineer

BMW M5 Concept

The latest BMW M5 uses turbocharging for the first time, which has helped to achieve 25-30% improvements in fuel economy

Tailpipe emissions: The twin-turboV8 will be quieter than the old V10 but emit far less CO2

BMW M division’s outgoing president Kay Segler explains why the previous BMW M5 used a naturally-aspirated V10 engine: to maximise marketing links with the BMW F1 engine programme of the time. So, given what a difficult business case it was to make, would it have existed had BMW not been in F1? Segler, who by now will have become president of Mini, chooses the diplomatic diversion: the future of the M5 is V8, not V10.

This time, it is not marketing that is dictating what engine the new M5 uses – but environmental concerns mean the M division still has outside influences. Carbon dioxide emissions reductions are a factor even for divisions boasting roots in motorsport, such as BMW M. 

“The M5 has to become relevant, has to be socially acceptable,” said Segler. “Drivers should not feel awkward when driving it.”

Significantly, this M5 will be turbocharged, for the first time in the model’s history. It is controversial to some M-car fans but turbocharging is, explained M’s head of R&D Albert Biermann, “The right technical concept for the time. The world is changing – we have to reduce CO2, yet still provide excellent performance. Turbocharging allows us to do this.”

BMW is claiming economy improvements of 25-30%, which equates to approximately 11 litres/100km with a corresponding reduction in CO2 emissions. Biermann said: “The turbo engine operates in a more efficient region in normal use, so gives much better fuel returns, particularly on lighter loads. However, on full throttle, it still delivers all the expected power.” 

M customers showed no resistance to turbocharging, claimed Biermann. “Besides, any initial resistance to the idea of turbocharging was made history once people experienced the X5 M SUV and 1 Series M Coupe,” he said. Experience of these cars has been instrumental in switching to turbo for the core M5. BMW has retained the expertise from its past turbocharging programmes, including the F1 programme of the 1980s. “Paul Rosche is still here – he knows everything about boosting. This helped us expand our core competencies, enabling us to learn and act fast,” said Biermann.

The new V8, known as the S63, is derived from the engine used in the X5 M and is a 4.4-litre, twin-turbo direct-injection unit. The turbos, each with twin scrolls, are mounted within the cylinder block’s vee. Biermann calls this “hot vee” and it makes the engine narrower and more compact.

An aid to lowering drive cycle emissions is the shortened distance between the combustion chambers and the catalytic converters – this improves light-off times, reducing fuel use on the NEDC test cycle.

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