Yet Another Spectacular 6-Cyl. Turbo from BMW

With 47 more ponies than last year’s winning B58 inline 6-cyl. turbo, the M340i’s engine never gasps for breath, no matter how much flogging occurs near the redline. And who would expect 25 mpg to go along with 369 lb.-ft. of torque?

Tom Murphy, Managing Editor

December 10, 2019

3 Min Read
bmw-twinpower-3.0L B58 turbo- - Copy
B58 engine enables BMW M340i sedan to reach 60 mph in 4.2 seconds with XDrive all-wheel drive.BMW

The 2020 Wards 10 Best Engines & Propulsion Systems are being revealed, in random, non-alphabetical order, one a day until Dec. 20. This is the second winner profile. 

A year ago, BMW had no trouble winning its 34th Wards 10 Best Engines trophy for its updated B58 3.0L turbocharged inline 6-cyl. in the new X5. BMW gasoline turbo-6s, including the B58’s predecessor, had won nine 10 Best trophies since 2007. 

Make that an even 10 with this year’s arrival of a high-output version of the B58. It really didn’t need improving, but Bavaria saw fit to add 47 hp and 39 lb.-ft. (53 Nm) of torque for application in the M340i sedan (pictured below), which is quite a bit lighter and more nimble than the X5 SUV. 

With 382 hp and 369 lb.-ft. (500 Nm) of thrust – available as early as 1,800 rpm – the latest iteration of the B58 (internal code name B58B30O1) wins a 2020 Wards 10 Best Engines & Propulsion Systems trophy with zero debate among judges and darn near perfect scores in the horsepower and torque categories. 

During staff test drives totaling more than 400 miles (644 km) shortly after Halloween – complicated by several inches of snow blanketing metro Detroit unseasonably early – the M340i’s DOHC 3.0L turbo-6 was ready for anything and never once gasped for breath, no matter how much flogging occurred near the redline. 

“The car’s no slouch no matter what mode you drive in (EcoPro – hah!),” editor Bob Gritzinger writes on his scoresheet. “Punch up Sport Plus, hammer the accelerator and hang on.” 

BMW M340i front blue - Copy.JPG

BMW M340i front blue - Copy

Speaking of EcoPro, BMW offers this as one of several driving modes to maximize coasting, stop/start functionality and brake regeneration, while stiffening the accelerator pedal. Someone buying a 382-hp German sport sedan might ask, “Why?” 

Having driven hundreds of miles in BMWs in recent years, I’ve come to appreciate EcoPro during steady-state driving on the highway – the casual cruiser mode – to conserve fuel. Few others on staff spent much time in EcoPro mode, and yet most judges remarkably topped 25 mpg (9.4 L/100 km) during our testing. 

Enabling both fuel efficiency and an eagerness to run hard are several upgrades specific to this version of the B58 engine in the M340i: 

  • 25% reduction in turbo impeller mass for quicker response. 

  • New twin-scroll turbocharger integrated into steel exhaust manifold for faster response and more power. Previously, exhaust manifold and turbo were two separate items. 

  • Lower compression ratio to offset greater turbo boost. 

  • New high-precision direct injection operating at 350 bar of pressure (5,076 psi), up from 200 bar (2,900 psi) in previous 340i sedan. 

  • New dual-branch exhaust system. 

  • New eighth-generation DME 8.6T.1 engine management.  

  • Split cooling circuits – low temp for air-to-liquid intercooler and high temp for engine cooling. 

  • One-piece timing chain reduces friction compared to previous two-piece timing chain. 

Overall, the engine benefits from improved cooling and reductions in component weight, internal friction and emissions. This engine, in the same state of tune, also appears in BMW’s Z4 M40i roadster and ’20 X3 M40i and X4 M40i CUVs. 

BMW M340i test driving.jpg

BMW M340i test driving

Relative to the previous 340i sedan, specific output rises to 127 hp/L from 107 hp/L, while compression ratio drops from 11.0:1 to 10.2:1. 

The M340i is rated at 22/30 mpg (11.8-7.8 L/100 km), a gain of 1 mpg (0.4 km/L) in city driving over the 340i.  

And yet, the M340i is more than a half-second faster accelerating to 60 mph (97 km/h), at 4.2 seconds with XDrive all-wheel drive and 8-speed ZF automatic transmission and running on premium fuel.  

Stretching its legs, the M340i exhibits a glorious, throaty exhaust note, especially when cycling through gears with paddle shifters. 

“BMW drops the equivalent of a Russell Westbrook triple-double on the rest of the industry with this awe-inspiring turbo inline-6,” editor James Amend writes on his scoresheet. 

BMW M340i 3.0L turbocharged 6-cyl. - resized.JPG

BMW M340i 3.0L turbocharged 6-cyl. - resized

About the Author(s)

Tom Murphy

Managing Editor, Informa/WardsAuto

Tom Murphy test drives cars throughout the year and focuses on powertrain and interior technology. He leads selection of the Wards 10 Best Engines, Wards 10 Best Interiors and Wards 10 Best UX competitions. Tom grills year-round, never leaves home without a guitar pick and aspires to own a Jaguar E-Type someday.

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