New 2021 BMW M4 sheds more camouflage at the Nürburgring

But as M division officials have revealed to Autocar, “it is for all intents and purposes an all-new drivetrain with significant changes to the base engine that allow it to rev beyond 7000rpm and deliver a much higher specific output” than today’s S55 engine. 

As well as being earmarked for the next M4 coupé and the M4 Gran Coupé, the new twin-turbocharged straight six is also planned to propel a new M4 Convertible, the upcoming sixth-generation M3 and, in a lesser-powered form, the second-generation BMW M2. It has been launched in the new X3 M and X4 M SUVs. 

An increase in power provides the new S58 engine with a higher specific output in Competition guise than the old S55 with water injection, a set-up used by the 493bhp M4 GTS. 

That unit provides the outgoing M4 coupé with 425bhp in standard guise and 444bhp in Competition form. 

BMW’s M division engineers have managed to raise power by more than 11% in the standard M4 and 13% in the Competition, with claimed outputs of 473bhp and 502bhp respectively. 

These figures appear set to place the new model in direct competition with the 444bhp Audi RS5 and 503bhp Mercedes-Benz C63S Coupé. 

Torque is also increased by 37lb ft, with the S58 engine delivering 442lb ft on a band of revs between 2600rpm and 5600rpm. 

Despite the increase in performance, the S58 engine has been developed to meet strict new emission regulations to potentially provide the standard M4 with a CO2 figure of less than 200g/km, thanks in part to the adoption of twin Otto particulate filters. 

Key among the changes over the S55 engine is the adoption of a longer stroke, at 90mm. The bore measurement remains 84mm, but BMW M claims the altered internal measurements help to boost torque potential. 

Also included are two mono-scroll turbochargers in place of the single twin-scroll unit used on the B58 engine, as well as BMW M’s latest Valvetronic variable valve timing and ‘Double Vanos’ variable camshaft profile. The compression ratio has also been reduced, from 10.2:1 for the S55 to 9.3:1. 

Although the new engine goes without water injection, officials say it may appear on a further-developed version of the S58 unit that is likely to appear in a successor to today’s 453bhp M4 CS. 

Secrecy surrounds the rest of the M4’s mechanical make-up. However, insiders suggest it is in line to abandon tradition by adopting a conventional eight-speed automatic gearbox and a similar xDrive four-wheel drive system to the latest M5 (with an M-Dynamic mode apportioning power to the rear wheels) in at least one version. 

It is also suggested a cheaper and lower-powered entry-level model could potentially be offered, with a manual gearbox and rear-wheel drive.

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