First look: 2014 BMW M3 and M4

The BMW M3 is back, faster and more powerful than ever before -- but only as a four-door sedan. For its iconic 3-series-based performance model, BMW will dispense with a 26-year tradition of high-revving naturally aspirated engines in lieu of turbocharged six-cylinder power.

Revealed here in production-car guise for the first time, the new 425-hp M3 sedan will be joined at the outset by its sister model, the M4 -- a mechanically identical but stylistically sleeker two-door coupe previewed in lightly veiled concept-car form at the Pebble Beach concours in California last August.

The new M3 sedan and M4 coupe will go public at the Detroit auto show prior to the start of North American sales in May 2014. Prices are yet to be announced, though officials have said they are likely to rise over previous models.

Both cars will be powered by the same twin-turbocharged inline six-cylinder direct-injection gasoline engine. The 3.0-liter unit is based around the German carmaker's familiar N55 engine, with 84.0 mm bore and 89.6 mm stroke measurements. BMW's M division said that the changes to the aluminum block, cylinder head, induction and exhaust systems and internal architecture are enough to classify the engine as all-new.

BMW
The new BMW M3 sedan will debut at the Detroit auto show.

The engine will feature BMW's patented induction process known as M TwinPower Turbo. It uses two low-inertia turbochargers running a maximum 1.3 bar of boost pressure and fed by a innovative water-to-air intercooler system mounted atop the engine. Meanwhile, weight-saving features, such as a magnesium sump, see the new engine tip the scales 22 pounds under that of its predecessor, at a claimed 452 pounds.

With 425 hp developed between 5,500 and 7,300 rpm and 406 lb-ft of torque between 1,850 and 5,500 rpm, the blown six delivers 11 hp and 110 ft-lb more than the naturally aspirated 4.0-liter V8 direct-injection gasoline mill it succeeds. An impressive 143 hp per liter -- some 38 hp per liter more than its predecessor through the effects of forced induction -- also gives it the highest specific output of any series production M division engine to date.

With familiar M division technology, such as Valvetronic variable-valve timing and Double VANOS continuously variable-camshaft timing, the new six-cylinder revs to 7,600 rpm -- 600 rpm less than the V8 it replaces.

While billed as the most powerful series production engine to find its way into the M3, the new inline six-cylinder, codenamed S55 B30, is the smallest capacity engine used by BMW's M division since the discontinuation of the first-generation M3's naturally aspirated 2.3-liter four-cylinder powerplant, the S14 B23, in 1991.

In combination with BMW's efforts to pare weight from its new performance-car duo through the use of new lightweight materials, the added reserves help improve the power-to-weight ratio of the M3 sedan by 22 hp per ton over its predecessor to 280 hp per ton. The new M4 coupe improves by a similar 22 hp per ton over the outgoing M3 Coupe to 284 hp per ton. By comparison, the latest Porsche 911 Carrera S boasts 283 hp per ton.

Channeling the drive to the rear wheels is a standard six-speed manual gearbox. The Getrag-produced unit has been developed from scratch and is claimed to be a 26 pounds lighter than the unit used in the outgoing fifth-generation M3. Among its features is dry sump lubrication, a double-plate clutch to handle the added torque loading, carbon-ceramic friction linings within the synchronizer rings and a blip function for downshifts. The individual ratios are shorter than before, with the final drive dropping from a previous 3.85:1 to 3.46:1 for added pace off the line.

Buyers will also be able to choose an optional seven-speed M Double Clutch Transmission (DTC), again from Getrag, with remote-paddle shifters. A development of the M5, it allows the driver to choose between manual or automatic modes. More features include launch control and a smoky burnout program -- the latter permitting a degree of wheel spin while the car is traveling at low speeds. To help improve on-the-limit handling, it also receives stability clutch control, which opens the clutches when sensors detect a loss of traction to reduce drive and bring it back in line.

Both gearboxes receive an automatic stop/start function, together with brake-energy regeneration and optimum-shift indicator. Despite BMW's earlier claims that the DTC unit is only 44 pounds heavier than the manual gearbox, the official weight figures reveal an 88-pound penalty.

BMW
The new 2014 BMW M4 is expected to join the M3 on the Detroit auto show stage.

In a new driveline development, the new M3 and M4 adopt a carbon-fiber-reinforced plastic propshaft. Constructed as a single component with no center bearing, it claims to bring a 40 percent weight saving on the previous M3's steel propshaft, while providing a reduction in rotating mass for improved driveline efficiency.

The new driveshaft is allied to hollow output shafts at the rear within the Active M differential, which continues to use an electronically controlled multiplate clutch to provide a varying degree of lock up between 0-100 percent, depending on prevailing traction.

BMW lists an official 0-60 mph time of 4.1 seconds in standard six-speed manual guise and 3.9 seconds with the optional DCT gearbox.

BMW says the new M3 and M4 will run the standing kilometer -- now an essential figure in performance claims among Germany's performance car elite -- in 22.2 seconds. As with all BMW M-division models, top speed is limited to 155 mph. An optional M Driver's Package raises it to 174 mph.

The improvement in straight-line performance is combined with a dramatic improvement in fuel economy. Official figures point to a combined cycle average of 26.7 mpg (U.S.) in manual guise and 28.3 mpg (U.S.) with the DTC gearbox on the European test cycle. The previous M3 sedan and M3 coupe boasted figures of 18.9 mpg (U.S.) as a manual and 21.0 mpg (U.S.) in DTC forms on the same test procedure.

The exterior styling changes over the 3- and 4-series have largely been driven by the need to provide the engine bay with added cooling capacity and a necessity to accommodate a widened chassis. The most significant visual modifications are centered around the front bumper, which receives an edgier design and three large ducts -- the outer units boasting BMW's so-called air curtains for more efficient air channeling.

Further alterations are directed at the hood, which receives a characteristic power dome to better accommodate the engine and provide adequate pedestrian crash protection, and the front fenders, which are more heavily flared and adopt a vent to extract hot air from the engine bay.

Further back, there are new two-tone exterior mirror housings and more substantial sills underneath the doors, while the rear receives widened fenders to house rear wheels that are wider in than those of predecessor models, as well as a re-profiled bumper with integrated vents to extract hot air from the rear differential and BMW M division's signature quad-tailpipe treatment.

In a continuation of earlier efforts to shed weight from its performance-orientated M division models, BMW has provided both the M3 sedan and M4 coupe with a carbon fiber reinforced plastic (CFRP) roof panel. The hood and front panels on each car are fashioned from aluminum. According to official figures, the M3 has dropped 187 pounds over its four-door predecessor at 3,351 pounds, while the M4 is 183 pounds lighter than the old M3 Coupe at 3,300 pounds.

The reduction in weight is significant, given that both of BMW's new M cars have grown in dimensions; the M3 sedan, codenamed F80, is 3.6 inches longer, 2.8 inches wider and 0.9 inch higher than before, while the M4 coupe, known internally as the F82, gains 2.2 inches of length and 2.6 inches of width, but is 1.7 inches lower than the outgoing fourth-generation M3 coupe.

While they rely on the same basic high-strength steel platform structure as the standard 3- and 4-series, the new M3 and M4 receive a largely bespoke chassis with reduced ride height and noticeably wider tracks, which have increased by 1.3 inches up front and 0.7 inch at the rear to 62.2 inches and 63.1 inches respectively to provide BMW's latest in a long line of M cars with a sporting stance.

The suspension, a traditional MacPherson strut (front) and multilink (rear) system, has also been extensively reworked, with lightweight components and new mounting processes claimed to have reduced unsprung masses and significantly boosted rigidity over the outgoing M3.

Key changes include the adoption of a substantial carbon fiber strut brace, aluminum control arms, wheel hubs and subframes up front, bringing about an 11-pound reduction in weight. The rear has also been extensively revised with aluminum control arms and wheel hubs and an axle that is bolted directly to the body without the use of rubber bushings, shaving 7 pounds.

“Mounting for the rear differential within the rear axle subframe, which is bolted to the body structure, has allowed us to achieve a new level of handling precision, but without neglecting comfort,” says Albert Biermann, BMW M division development boss, of the new cars.

The suspension supports standard 18-inch wheels -- 9 inches wide up front and 10 inches wide at the rear. They come shod with 255/40 profile front and 275/40 profile rear tires. Buyers can also choose optional 19-inch wheels with the same profile rubber.

An optional Adaptive M Suspension brings variable damping control in three different modes: comfort, sport and sport plus -- each of which boasts its own individual stability control calibration.

In line with standard 3- and 4-series models, the new M3 and M4 also receive an electro-mechanical steering system with a ServoTronic function that adjusts the level of assistance according to speed. Developed in partnership with ZF, it also offers the driver the choice of three modes at the touch of a button: comfort, sport and sport plus.

By Greg Kable