BMW is gradually replacing its N54 3.0-liter twin-turbocharged inline-six (featured in models like the 335i) with the firm's new twin-scroll turbocharged 3.0-liter inline six cylinder engine, designated N55. The latest Bavarian products to get the N55 are the 2011 model year 135i Coupe and Convertible that will go on sale in the United States in Spring 2010.
With a maximum output of 300HP at 5,800 rpm and a peak torque of 300 lb-ft available from 1,200–5,000rpm (U.S.-spec version), the new six-cylinder produces the same level of performance as the current twin-turbo six-cylinder.
However, BMW says that thanks to the adoption of the single, twin-scroll turbocharger and the integration of VALVETRONIC throttle-less intake technology, the new engine promises better throttle response and even more fuel efficiency.
In addition, the automaker claims that peak torque is reached 100rpm earlier than with the previous engine while engine boost response is improved across the entire engine speed range.
Both the 135i Coupe and Convertible will be optionally available with BMW's 7-speed Double-Clutch Transmission (DCT) that now features dedicated steering wheel paddles for upshifting (on the right) and down shifting (on the left).
For the 2011 model year, BMW also replaced the HiFi System Professional with a new Harman Kardon Surround Sound System while the climate control instrument unit features a new alignment and optics.