BMW M3 and M4: First official details

Due to be unveiled in Detroit in mid-January before going on sale in Australia in July next year, BMW’s all-new M3 sedan and M4 coupe will walk a fine line between low-end twin-turbo punch and free-revving high-end fun from their 3.0-litre six-cylinder powerplants.

After months of teasing, BMW has confirmed the rear-drive M3 and M4 mid-size performance models will boast 317kW of power, 550Nm of torque and will run to 100km/h in just 4.1 seconds, making them more than half a second quicker than before. Back in October, motoring.com.au predicted 316kW of power and “low four-second” 0-100km/h sprinting.

While the M3 sedan will carry five seats to the M4’s four, they will share the same 2812mm wheelbase and 4671mm overall length. Despite this, the M4’s weight has plummeted by 80kg to 1497kg, while the extra doors on the M3 push it up to 1520kg.

With the V8 gone from the M3’s engine bay (with a compensatory 40 per cent improvement in torque) and the two-door variant of the 3 Series now called the 4 Series, it’s all change for the smallest official M car, which will debut alongside the Lexus RC F coupe at Detroit.

BMW has tried to offset the low-end revving nature of twin-turbo engines by keeping the 2979cc inline six oversquare, with a bigger bore (89.6mm) than its stroke distance (84.0mm) so the motor will still rev beyond 7500rpm.

The engine, code-named S55B30, runs a high compression ratio (10.2:1) for a turbo motor, and both of its Honeywell turbos are monoscroll units with variable geometry, generating 1.25 bar more than the ambient air pressure.

BMW promises it will punch hard from low revs and keep spinning up high, which is reflected in its power and torque curves. The new engine, which could find its way into the smaller 2 Series for one-make racing, delivers its torque peak from 1850rpm all the way to 5500rpm and its power peak chimes in at 5500rpm and stays until 7300rpm. At 2000rpm, there is 70 per cent more torque than the old M3 engine.

It weighs 205kg fully dressed, which is 10kg below the outgoing atmo V8, but it’s so tall that M has to crank it over by 30 degrees to make it fit beneath the bonnet’s power bulge (yes, it’s actually needed this time).

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 g loads of more than 1.2g in any direction.

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

Besides being force-fed by two turbos, with cooling and lubrication systems set up with a bias to surviving hot laps of race tracks, the twin-turbo straight six has BMW’s usual tricks like direct fuel-injection, variable valve timing and lift, plus variable camshaft control on both cams.

It has given the M3/4 engine a mighty 106.4 kW per litre of power and gives the M4 a healthy 4.7kg/kW power-to-weight ratio. It’s this power-to-weight figure, coupled to improved aero performance, that delivers a standing kilometre in 21.9 seconds.

Besides power, the M4 is 25 per cent more economical than the outgoing M3 coupe, too, with the dual-clutch version delivering 194g/km for both the M3 sedan and the M4 coupe. That means no M3 since the 1986 version has had lower emissions than this one.

For the record, the 1986 M3 produced 143kW and 240Nm and emitted 192g/km of CO2, before the 1992 version increased that to 210kW, 320Nm and 275g/km and the 2000 model again lifted those figures to 252kW, 365Nm and 287g/km.

The outgoing 2007 M3’s 4.0-litre V8 upped outputs to 309kW and 400Nm, but lowered emissions to 263g/km, while the 2014 M4 more than doubles the power and torque of the original M3 yet emits only 2g/km more CO2.

Even so, a 60-litre fuel tank might be a bit small for some, especially as the car’s urban-cycle 12.0L/100km figure will be easily smashed during the track days BMW says it’s in-part designed for.

While the optional seven-speed dual-clutch transmission adds 40kg to both cars, it’s both faster (by 0.2 seconds to 100km/h) and more economical than the six-speed manual versions. The first part of that is due to its faster shifting and shorter gearing in its first four gears (both gearboxes are direct-drive in fifth) and the second part is due to its far taller top gear.

The manual, aimed at the US market as much as anywhere else, is derived from the 1M Coupe’s gearbox, but has had a twin-plate clutch, stronger gears and rev-matching added to it.

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.

The 435i’s suspension is already a significant upgrade over the 335i sedan, but the M3/4 has gone even further. The Ms have 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.

BMW has also stiffened up the front-end with a combination of forged aluminium suspension components and a thin, giant boomerang-shaped carbon-fibre strut brace, all accommodating M’s first electric 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 brakes include steel rotors with four-piston callipers at the front and two at the rear, though there is an optional 400mm carbon-ceramic disc with six-piston calipers up front and four at the rear.

The nett result is a set of track dimensions that are nearly two inches wider than the 435i’s (and are almost as wide as the M5’s), which demanded unique body panels everywhere. The only panels shared with the 435i are the doors, which let M push the front track (on both the M3 and M4) out to 1579mm and the rear track to 1603mm.

While the large rear three-quarter panel is steel, the bonnet and the front quarter panels are aluminium and the roof and 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/rear weight distribution, Wimbeck admits it was a close thing.

“The weight distribution is always a huge issue. 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 to 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 convertible.

“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.”

In Australia, the previous M3 sedan – at just under $150,000 -- was priced lower than the M3 coupe (about $155,000) and M3 convertible (about $173,000).

Direct rivals for the M4 include Audi’s RS 5 Coupe ($155,900) and the Mercedes-Benz C 63 AMG Coupe ($157,545).