Engine and gearbox
At a glance, the new engine doesn’t differ much from the one in the old M135i; both cars are described as using a turbocharged 3-litre straight-six. In fact the new engine is slightly bigger with a swept capacity of 2998cc rather than the old engine’s 2979cc. The new engine’s single twin-scroll turbo is now fractionally larger too, helping increase power by 14bhp to 335bhp. Torque is significantly increased as well, from 332lb ft to 369lb ft.
The new engine is a real joy to rev right to its 7000rpm rev limit; it doesn’t lose any energy as it gets close to the red line and it continues to emit a distinctly six-cylinder timbre. Sadly, it sounds best from outside the car.
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The standard gearbox is a six-speed manual, and it really suits the torquey nature of the new engine; there’s impressive acceleration, even in the higher gears. The gear change isn’t the slickest of actions; it feels too rubbery and the centre armrest puts your arm at an awkward angle. However, there’s a much greater connection to the drivetrain with the manual gearbox than with the optional automatic.
The eight-speed torque-converter auto available in the M140i is the same ZF gearbox as in the old car and in, well, almost everything. How this transmission behaves in different cars can be quite dramatic, but it’s rarely as faultless as it in these BMWs; it’s so incredibly easy to adapt to while also effecting quick, direct changes. It can be a bit too abrupt though, and in the wet the severe changes can cause the rear tyres to lose traction.