.The most significant updates come underhood, where the much lauded twin-turbocharged 3.0-liter inline-six is being replaced by a new single turbo version. The revised engine, dubbed N55, has recently been launched in the 740i and the 535i Gran Turismo. The twin scroll turbo has dual exhaust inlets that allow the engineers to better balance the pulses coming in to spin up the turbine faster. This is expected to reduce the turbo lag that some drivers complained about with the outgoing twin turbo setup.
BMW also claims it has reduced cold-start emissions by routing all the exhaust gases through a single, larger catalytic converter that heats up faster. On the intake side, the throttle is eliminated thanks to the addition of BMW's Valvetronic variable valve control system. The N55 also gets direct fuel injection. The end result is the same 300 horsepower and 300 pound-feet of torque as before, but with a fatter torque curve that maintains its peak from 1,200-5,000 rpm
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