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BMW reveals tech behind upcoming M3 and all-new M4 coupe

25th Sep 2013 9:34 pm

Here's a look at the engine and other technology used in BMW's M3 saloon and M4 coupe.


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.       
Although BMW M division isn’t prepared to go public on the official torque figure some three months prior to a planned public premiere for the new M3 and M4 at the 2014 Detroit motor show, it does confirm the S55 B30 delivers “significantly more than 51kgm at well under 2000rpm”. By comparison, the non-turbocharged S65 delivered 40.78kgm at 3900rpm.
BMW M division development boss, Albert Biermann, describes the added torque as being “central to performance gains” for the new M3 and M4. He points to a 70 percent improvement in the torque loading of the new engine in comparison to its predecessor at 2000rpm. This leads to improvements in real world performance, with in-gear acceleration claimed to be greatly enhanced. There is no official 0-100kph time yet, but Autocar has been told the M4 coupé will undercut the official 4.8sec time of the old M3 coupé “by some margin”, suggesting a time in the region of 4.5sec. Top speed, as with all M-cars, will be limited to 250kph in standard guise.
At the same time, BMW’s M division suggests the new M3 saloon and M4 coupé will be certified with average CO2 emissions “under 200g/km” on the European test cycle – or a whopping 90g/km plus reduction on the old M3 coupé. This indicates combined cycle consumption of over 14kpl, thanks in part to the inclusion of a stop/start function and brake energy recuperation.
Despite the similarities in specification between the new BMW M3 and M4’s engine and that of the earlier 1-series M coupé, Biermann reveals the two engines share little apart from their bore and stroke measurements. “They are completely different, not only in construction but internally and their respective induction processes. They’re worlds apart.”
At the heart of BMW M division’s new twin-turbocharged 3.0-litre in-line six-cylinder, which is mounted longitudinally, is a patented induction process that uses two low internia turbochargers. Eschewing both twin-scroll and variable vane geometry, the IHI produced units provide a relatively conservative maximum boost pressure of just 1.3 bar. “There’s nothing particularly groundbreaking about the turbochargers themselves.
But the induction system is significantly more free-flowing, with greater volumes and a faster transfer of air through the entire system, than with either the 1-series M engine or BMW’s regular turbocharged 3.0-litre engine,” says Biermann.
BMW’s M division engineers have mounted the water-to-air intercooler system for the turbochargers atop the engine instead of out in front, justifying the inclusion of a prominent power dome within the bonnet. Weight saving features such as a magnesium sump ensure the new engine weighs 10kg less than the naturally aspirated 4.0-litre V8 direct-injection petrol unit it supplants at a claimed 205kg.
The engine's heady reserves are channelled to the rear wheels via a standard six-speed manual gearbox. A development of the ZF-produced unit used in the 1-series M coupe, it uses a newly designed twin plate clutch to handle the added torque loading and is claimed to weigh 12kg less than the similarly specified gearbox used in the fifth-generation M3.
A development of the existing Getrag-produced seven-speed dual clutch Drivelogic gearbox with remote paddle shifters will be available as an option, providing the M3 and M4 with automatic shift capability and a launch function. Described as a third-generation unit, it adopts a raft of changes that Biermann, suggests provides it with “vastly improved shift quality”.
A further development brought to the M3 and M4’s driveline is a new singlepiece carbonfibre reinforced prop shaft. Claimed to weigh 40 per cent less than the all steel unit used on the old BMW M3, it brings a reduction in reciprocating masses and what BMW M division engineers are flagging up as sharper response. It acts on a reworked M differential that now uses an electric actuator to constantly vary the locking effect.
As on the M5 and M6, it is capable of delivering 100 per cent lock up. Biermann suggests the new driveline components bring about improved traction and on-the-limit adjustability.
Underpinning the M3 and M4 will be a common chassis boasting unique track widths, forged aluminium suspension components, heavily revised elasto-kinematics and a rear axle supported by a new steel carrier that, unlike that of the old M3, is bolted directly to the body, without the use of traditional rubber bushings. The new carrier is claimed to provide added lateral rigidity, leading to what Biermann describes as “extremely precise wheel control and a reduction in roll steer.”
Overall, some 8kg have been pared from the standard 3- and 4-series' suspension – 5kg of that up front, and a further 3kg at the rear. Unsprung masses are also claimed to have been reduced through the adoption of unique suspension components. Among the engineers responsible for the fine tuning of the handling is Arnd Meyer, who joined BMW's M division from Mercedes-Benz's AMG offshoot late last year.
Official figures are not yet being made available but the overall footprint of the new M3 and M4 is significantly larger than that of either the standard 3- or 4-series, requiring the use of widened fender panels to house forged aluminium wheels of up to 19-inch diameter shod with  255/35 ZR 19 front and 275/35 ZR19 rear Michelin Pilot Super Sport tyres.
The steering is an electro-mechanical system, which is a first for the M3. “Our mission is to provide the best electro-mechanical steering. There is no doubt: it is better than the hydraulic system of the old M3,” boasts Biermann.
As with the latest M5, the driver can choose between three different driving modes: Efficiency, Sport and Sport Plus. Each mode provides differing mapping characteristics for the steering, throttle, gearbox (on models equipped with the optional seven-speed dual clutch unit) differential and threshold of both the traction and stability control systems. The damping also boasts three modes: Comfort, Sport and Sport Plus.
Meanwhile, BMW has revealed both the new M3 saloon and M4 coupé will feature a carbonfibre-reinforced roof panel. The bonnet and front fenders are aluminium pressings with the doors and rear fenders made of steel.
Copyright (c) Autocar UK. All rights reserved.

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