BMW M3 and M4 get straight sixes

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In BMW’s opinion, the engine powering its two latest M cars, the M3 and M4, sets a new high point in terms of output and torque for six-cylinder, in-line gasoline units. Specifically, the power unit offers 60bhp more than the maximum output of its predecessor models and an increase in peak torque by 100Nm.

The company claims its 3.0-liter straight-six engine combines the high-revving character of BMW M engines with the latest version of its M TwinPower Turbo technology. As a result, 650Nm of torque is available between 2,700rpm and 5,500rpm, with power sustained at 510bhp from this RPM up to the 7,200rpm red line.

The turbocharging system consists of two, mono-scroll turbochargers that supply cylinders 1–3 and 4–6 respectively. A charge cooler keeps inlet temperatures under control while an electronically controlled wastegate governs boost pressure. BMW notes the engines also feature its Valvetronic system for variable valve timing.

Recognizing that many owners will take their cars on track, the company says the cooling system has been developed to ensure efficient cooling even under heavy-duty cycles, with the system split into low-temperature (for the charge cooling) and high-temperature circuits (for the block and turbos).

The oil system has also been designed with track use in mind, with the sump featuring two separate chambers and an integrated suction channel, while an additional suction stage on the pump allows the oil pump to draw lubricant from the smaller chamber when extra capacity is needed.

Both M models use a version of BMW’s 8-speed M Steptronic transmission produced by ZF, with a variety of drive modes tailored to the performance nature of the cars.

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Lawrence has been covering engineering subjects – with a focus on motorsport technology – since 2007 and has edited and contributed to a variety of international titles. Currently he is responsible for content across UKI Media & Events' portfolio of websites while also writing for the company's print titles.

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