BMWs, particularly those from their high performance M division, are intrinsically linked to the inline-6 engine. More recently these have shrunk slightly in displacement and adopted turbocharging for higher outputs and lowered emissions, but are inseparable from the BMW recipe nonetheless.
In the X3M and X4M, the sports SUV pair debuted the German automaker’s most potent version yet of their 3.0-litre sixer, one capable of dispensing up to 375kW, even edging out the BMW M4 GTS and its S55 twin-turbo unit with a motorsport-derived water injection system.
For the upcoming version of the M3 and M4, due in 2020, the innovations carried in these newer breed of engines will trickle into their next-generation of more bespoke six-cylinder motors. With beefier internals and higher tolerances, Autocar reports that power projections sit healthily above 373kW.
Internally called the S58, the new straight-six will obviously be based on the B58 that currently powers a plethora of BMW’s more vanilla cars and SUVs, and is expected to debut in the next M4, but one that wears a sleek four-door Gran Coupe body.
Derivatives of this purported S58 will also slot into the M4 coupe and cabriolet as well as the M3 saloon, which itself is based on the G20 3 Series. Also twin turbocharged, the specific output will be a good deal higher than the current S55, naturally, but also engineered to operate optimally at higher revs well beyond 7000rpm.
One of the central factors that result in the increased power over the outgoing S55 is the longer 90mm stroke, a reduced compression ratio, a reworked twin-turbocharger array, and optimisation of the the forced induction system with the BMW’s Valvetronic variable valve timing and Double Vanos variable camshaft profile. This is all in spite of the engine’s mandatory adherence to the stricter WLTP emissions regulations.
From there, BMW also has plans to spread the new motor around the M range with a prime candidate being the next-generation M2 and M2 Competition. At this stage, expecting anything larger to be worthy of a M badge would require V8 intervention, and indeed the F90 M5 as well as the upcoming M8 and M8 Gran Coupe, with its standard all-wheel drive system, does/will make full use of the updated S63 eight-pot displacing 4.4-litres.
As for more details on the next-generation M3 and M4’s shared powertrain, it remains unclear whether the pair will continue to use a dual-clutch transmission and maintain a rear-wheel drive configuration in light of BMW’s recent preference of ZF’s versatile 8HP torque converter automatic and the improved standing acceleration and all-weather ability afforded by M xDrive.
However, brand purists are probably hoping that BMW will steer clear of both these directions in favour of a more ‘traditional’ set of ingredients and a lighter car overall. There’s still plenty of speculation surrounding a possible ‘Pure’ variant of the all-new M3 and M4 with less equipment, rear-wheel drive, a manual transmission, and a correspondingly reduced starting price.