Official: BMW ditches V8 for M3 and M4

BMW has confirmed one of the automotive industry’s worst-kept secrets by announcing it will ditch V8 power in favour of a mostly new six-cylinder engine for its new M4 coupe and M3 sedan.

But it won’t be any old six-cylinder engine, with BMW promising track-pack handling and blistering point-to-point speed from its new M3 and M4, first technical details of which have now been revealed.

Due to be launched officially at the Detroit motor show in January before they go on sale here next May, the M3 sedan and the M4 coupe will deliver 316kW of power from their mostly new twin-turbo 3.0-litre in-line six-cylinder engine, which will be enough to accelerate them to 100km/h in the low four-second bracket.

The lightest versions will slide beneath 1500kg, helping to record sub-200g/km CO2 emissions figures, and BMW has also promised “well in excess” of 500Nm of torque to help shove them around.

Even though the 435i’s suspension was a significant upgrade over the 335i sedan, the M3/4 has gone even further. M has developed unique front and rear suspension hardware, with the rear-end’s five-link system attaching to a steel subframe that bolts directly to the body.

It has stiffened up the front-end with a combination of forged aluminium suspension components and a thin carbon-fibre strut brace that looks like a giant boomerang, all accommodating M’s first electronic power steering system.

Holding up the standard M3 and M4 will be a set of 19-inch forged alloy wheels clad in Michelin Pilot Super Sport 255/35 ZR19 tyres at the front and 275/35 ZR19s at the rear.

The standard brake package will include steel rotors with only four calipers at the front and two at the rear, though there is an optional 400mm carbon-ceramic disc with six-piston calipers at the front and four-piston units at the rear.

The net result is wheel track dimensions that are nearly two inches wider than the 435i’s (and almost as wide as the M5’s) and demanded unique body panels everywhere. The only panels shared with the 435i are the doors.

While the large rear three-quarter panel is steel, the bonnet and the front quarter panels are aluminium and the roof and the boot (including the aero-friendly Gurney bubble) are made from carbon-fibre.

“We didn’t aim for the previous-generation M3 as the target weight,” M’s Michael Wimbeck said. “We aimed at the previous, previous generation that was 1495kg.”

While the M3 and M4 will retain M’s signature 50:50 front-to-rear weight distribution, Wimbeck admits it was a close thing.

“The weight distribution is always a huge issue. At the rear you usually find parts that are light or easy to make light. It is harder at the front.

“Generally it’s 50:50. It’s easier to find parts at the rear of the car to make the car lighter but then you have to chase more and more expensive parts in the front to keep the balance.”

M’s head of engineering, Albert Biermann, expects more than 60 per cent of combined sales will go to the two-door M4, with 30 per cent for the four-door M3 and between five and seven percent for the upcoming M4 Cabriolet. There will be no Touring version, as M sees the wagon as a Europe-only body style, and even then mainly a German and British machine.

“The four-door was really a bargain in the US in the last generation,” he said.

“From the technical substance, again, there will not be a significant difference between the coupe and the sedan so it depends on how markets price it if it will be a bargain again.”

All models will be available with the choice of a new, stronger six-speed manual (derived from the 1M Coupe’s ‘box, but with a twin-plate clutch, stronger gears and rev-matching added) or a dual-clutch automatic that is actually faster but adds around 30kg.

The manual gearbox is unashamedly aimed at US customers, with Biermann pointing out that more than 20 per cent of M3 buyers there insist on changing their own gears.

To get this drive to the rear differential, with its in-built locking unit that now has a drift-recognition system that switches the diff to fully locked, M developed a one-piece, carbon-fibre propshaft that adds stiffness, reduces rotational inertia and saves 5kg.

While Audi Quattro and Mercedes-Benz’s AMG divisions continue to pursue all-wheel drive, Biermann said the junior Ms will remain rear-drive, even into the next full generation.

“To accelerate out of corners, it is so fantastic with this concept that it’s not needed.

“People quote Audi, but look at Audi. They have no possibility to make a rear-wheel drive car so they might as well do all-wheel drive.”

M has confidence that the chassis will impress buyers, but knows they will always come for the engine.

Loosely based on the 1M Coupe’s six-cylinder engine, the S55B30 unit will rev beyond 7500rpm, even though the torque peak will be available from around 2000rpm and the power peak arrives around 5000rpm and holds to 7300rpm.

BMW insists on calling it a high-revving engine, though the torque curve indicates a flat, early performance delivery rather than the sweet spinning of the outgoing motor.

Weighing 205kg fully dressed, the engine is 10kg lighter than the V8 it replaces, even with its pair of Honeywell turbochargers and indirect intercooling system attached. The two turbos generate around 1.25 bar more than the ambient air pressure, which is then fed through the intercooler into chambers with an 80mm bore and an 89.6mm stroke.

M has to cant the engine over at a 30 degree angle to make it fit beneath the bonnet’s power bulge, but it delivers 70 per cent more torque than its predecessor at 2000rpm and 40 per cent more at 7500rpm.

There’s a closed-deck crankcase, a magnesium oil pan and a forged-steel crankshaft, with the engine’s oil circuit designed to cope with sustained loads of more than 1.2g in any direction.

The turbochargers don’t use twin-scroll technology, but combine with variable valve timing and lift and direct fuel-injection to deliver more power than ever before in an M3 but with emissions around 30 per cent lower than the E36 M3 of 1992.

Although peak power is only 7kW up on its predecessor’s 309kW 4.0-litre V8, torque will rise from 400Nm by more than 100Nm. The last six-cylinder M3, the E46 of 2000, produced 252kW and 365Nm.

There are four exhaust pipes too, all of which are permanently open, though an electronically activated flap can short-circuit a rear silencer at the push of a button for more sound.

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