martinbo
Staff member
View the Post on the BlogWith the M4 Concept publically absent from the recent Frankfurt Motor Show, BMW have been quick to appease disappointed fans with the release of key technical information regarding the new BMW M3 Sedan and M4 Coupé siblings thereby laying to rest years of intrigue and speculation.
In Summary
The new BMW M3 and M4 will make use of an all-new, twin-turbocharged inline six cylinder engine specifically developed by BMW's M GmbH division to operate at the levels required of a high performance powertrain. Code-named the S55B30, this high-revving engine is mated to both a six-speed manual gearbox (hurrah for BMW!) or an optional M-DCT dual-clutch transmission with the familiar quota of seven forward ratios. Key outputs are quoted as "more than" 320 kW and 500 Nm. Power is directed to the rear-wheels via a newly developed carbon-fiber propeller shaft - featuring substantial weight savings over the previous iron propshaft - with drive split left-to-right by a new electronically actuated limited slip "Active M Differential".
Much emphasis has been placed on the reduction of weight with BMW claiming a weight of under 1500 kg through a program focused on reducing both mechanical and bodywork component mass. Carbon-fiber Reinforced Plastic (CFRP) makes up the roof material composition for both the saloon (for the first time as standard) and the coupé derivatives.
Underpinning the new M-twins is a purpose-engineered suspension solution featuring a new rear subframe assembly bolted directly to the monocoque combined with the extensive use of aluminium componentry at both the front and rear axles. An all-new electro-mechanical power-steering mechanism is employed in the M3-M4 for the first time too.
In keeping with the now familiar approach, electronic wizadry allows drivers to tailor the driving characteristics of the vehicle via systems such as the variable steering settings, M-Dynamic Mode and the optional Adaptive M suspension. All of this adds up to making the new M3 Sedan and M4 Coupé exceptionally usable and dynamic on both road and track.
Pricing for the new M3 and M4 models has yet to be released. Click on more below for additional details.
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The Engine
It's always big news when the specifications of an all new M Car are released and this case is no exception. The internet rumours of the new M3/M4's engine being nothing more than a hotted up N55 are immediately dispelled. The S55B30 follows on the tradition of S-designated engines being substantially different from those in regular BMWs. The mechanical differences between the N55 and S55 are extensive to say the least.
The turbochargers (for so long an area of lengthy speculation) are a new design; they forego twin-scroll turbocharging - it was obvious that this would be the case as 6 (cylinders) divided by 4 (scrolls) doesn't give a whole number - for a simpler mono-scroll layout fed by a short-path manifold. It's a simpler, more conventional approach that eschews complexity like variable vane technology but still achieves excellent spool-up response and high-rpm volumetric flow. Each turbo is fed by 3 cylinder exhaust outlets and their waste gate mechanisms are controlled by electric motors. Maximum boost pressure is said to be 1.25 bar but BMW claim that this full level of boost will hardly be required - the S55B30 will be able to run optimally in moderate conditions without the need for maximum boost. This enhances durability and ensures sufficient operating contingencies at higher temperatures and altitudes. The turbos compress air into a relocated, charge air (water-to-air) intercooler which is placed so as to reduce the length of the tract to the inlet manifold.
The crankcase is newly engineered as a closed deck design to cope with the rigours of high-performance operation. It houses another all-new component: a lighter forged crankshaft quite separately conceived from the cast crank in the N55. Specialised, lightweight pistons and connecting rods make up the remainder of the reciprocating componentry.
A bespoke oil circulation management system comprises of a new scavenger oil pump within the magnesium sump to ensure optimal circulation for both the engine and turbochargers in order to cope with the demands of high-G lateral and longitudinal acceleration. The familiar systems of High Precision Direct Injection, VALVETRONIC variable valve timing and Double-VANOS complete the S55B30's technical repertoire. All of this adds up to generate outputs of more than 320 kW and 500 Nm of torque from an engine said to weigh 10 kg less than the S65 V8 in the E90/92 M3.
Drivetrain
The six speed manual gearbox is a successive development of the ZF unit engineered for the previous generation M3. In this application, however, the transmission has been lightened by as much as 12 kg over its forebear and features improved shift quality by virtue of carbon-coated synchroniser rings. Another manual gearbox feature new to the model is automatic throttle blipping on downshifts which matches engine rpm to geared speeds for smoother down changes. Hopefully this feature can be disabled by those of us who spent hundreds of hours getting the heel-n-toe technique right. All in all, BMW have to be lauded for continuing to offer a manual gearbox on the new M3 and M4.
A 7-speed dual clutch M-DCT transmission is optional. This unit brings Drivelogic and Launch control features to the fore and will no doubt provide swifter acceleration and faster response in any equivalent gear over the manual gearbox whilst offering the driver a series of selectable modes to suit both mood and situation alike.
Another component new to the M-Car stable is the carbon-fiber propshaft which, once again, provides for gains in the weight-loss department. No universal joint is required as a result and a 40 percent reduction in the mass of this component is claimed. The drivetrain is completed via the implementation of a new variable Active M Differential which makes use of an electric motor to control the amount of differential lock required based on the demand for traction.
Suspension
The suspension has undergone significant re-engineering and sees an extensive application of aluminium (not employed in the standard F3x derivatives of the 3 Series) at both the front and rear axles. Control arms in aluminium fore and aft reduce unsprung mass and improve wheel articulation response whilst the all-new aluminium rear axle subframe mounts directly, unbushed, to the body via bolts ensuring as little slack in the system as possible. All of this contributes to sharper, more direct vehicle dynamics. Clearly the suspension rework is not only significantly different from that used in the standard 3 and 4 series models but it's also commensurately in keeping with what is expected from an M Car.
Bodywork
A CFRP roof panel now features as standard fitment on both the sedan and coupe derivatives for the first time. It reduces roof mass by 5 kg and provides for a lowered centre of gravity. A CFRP strut brace is employed in the engine.
So - there you have it - for all of those naysayers who thought that BMW's next M Car would not be sufficiently differentiated from its mainstream donor models: think again. The new BMW M3 Sedan and M4 Coupé display significant technical differentiation from the regular 3 Series and 4 Series models thereby ensuring that this new M3 (and now, M4) will be every bit as special as their illustrious predecessors.
