BMW’s M division has officially confirmed that a new in-line six-cylinder engine is bound for its upcoming M3 saloon and M4 coupé and convertible.
The brand has revealed a potent twin-turbocharged 3.0-litre direct-injection petrol unit that produces an official 424bhp at 7500rpm and what officials describe as “significantly more than 51kgm” of torque.
The newly developed engine, known under the internal codename S55 B30, shares its 84.0mm bore and 89.6mm stroke with BMW’s standard turbocharged 3.0-litre in-line six-cylinder direct injection petrol mill, the M55. That engine is used across the German manufacturer's line-up, endowing the aluminium block unit with an overall swept volume of 2979cc.
This represents a sizeable 990cc reduction on the engine BMW’s M division’s new unit replaces, the S65.
The 4.0-litre V8 direct-injection petrol unit, the last in an illustrious line of traditional naturally aspirated engines from BMW’s revered M division, has been resigned to the history books after just six years of service in the outgoing fourth-generation M3 coupé, saloon and convertible in a continuation of an engine downsizing program.
Despite the 25 percent reduction in capacity and the loss of two cylinders, the new BMW M division engine delivers 10bhp more than its predecessor thanks to a patented induction process that is claimed to provide vastly improved levels of combustion efficiency.
In the process, BMW is also preserving an illustrious 27-year tradition that has seen each incarnation of the M3 boast more firepower than its direct predecessor. But while the new S55 B30 develops its maximum power of 424bhp at 7500rpm, the old S65’s 414bhp arrived at 8300rpm. With 142bhp per litre, the new twin-turbocharged six-cylinder engine betters the specific output of the old naturally aspirated V8 by a substantial 38bhp per litre.
As a measure of its overall efficiency, it also develops 16bhp per litre more than the twin-turbocharged 4.4-litre V8 direct injection petrol engine used by the recently facelifted BMW M5 as well as the M6 coupé, cabriolet and Gran Coupé. The ignition cut out is yet to be officially revealed, although officials suggest it will be pegged at 7600rpm.
Among the technical highlights for the new BMW M division engine is its closed deck design for added rigidity. It also uses a spray coating instead of traditional cylinder bore liners for reduced weight. A forged crankshaft is also used for reduced rotating masses, which, in combination with lightweight pistons, is claimed to bring about a significant improvement in throttle response compared to BMW’s standard turbocharged 3.0-litre in-line six-cylinder petrol engine.
With BMW’s M division claiming an overall weight of “just under 1500kg” for the new M4 coupé, which uses selected carbonfibre reinforced plastic panels and bracing components as part of a weight-saving initiative, the new two door promises to boast a power-to-weight ratio better than the discontinued fourth-generation M3 coupé’s 262bhp per tonne. Nothing’s official, but Autocar has been told to expect somewhere in the region of 284bhp per tonne.
An even lighter version of the new sports car, possibly resurrecting the famed CSL nomenclature and fitted with lightweight seats as part of a pared-down interior and other weight-saving measures, is under consideration for sale later in the new M4’s model cycle. BMW M division boss, Freidrich Nitschke, suggests it could come in close to 1400kg if it receives a production greenlight.
