Adding Another Pair of Turbochargers, as well as six cylinders to this year's rankings, BMW AG's 3.0L twin-turbocharged I-6 achieves its third-consecutive spot on the Ward's 10 Best Engines list.
Arguably one of the best volume internal-combustion engines ever produced, the wonderful straight-6 turbo, along with BMW's 10 Best Engines-winning 3.0L clean diesel, support the auto maker's new direction to use advanced compressors and fuel-injection technology to extract the best performance and efficiency from its Ultimate Driving Machines.
The engine serves as BMW's answer to competitors' larger-displacement, normally aspirated V-6s, with the two fast-spooling turbochargers helping produce more low-end torque than the Ford Mustang GT's 4.6L V-8 of similar power.
And because of direct-gasoline injection and relatively low boost pressures, there virtually is no noticeable lag in power delivery, just immediate surges of thrust.
Hardly any negative comments made it on to the judges' evaluation sheets this year, with a few minor protests noting observed fuel economy could have been better.
However, given the spirited performance of our 135i Coupe tester, as well as the lustful crescendo of sound emitted as rpm climbs, the BMW is difficult to drive moderately enough to maximize efficiency.
When pressed, though, the 135i easily achieves — and occasionally surpasses — its 25-mpg (9.4-L/100 km) U.S. Environmental Protection Agency highway rating.
This engine is extremely capable, whether in a sports car or in a cross/utility vehicle, and advanced enough to remain relevant for years.
Output easily could be increased beyond the current 100 hp/L and the likely near-term inclusion of start-stop and hybrid-electric capability greatly will improve fuel economy.
But it is the performance of BMW's turbo-6 that once again garners the most praise, with the usual superlatives dominating water-cooler banter and the final tallying of scores.
While the price of entry is a tad steep ($35,600), it's hard to argue with the 135i's 5-second 0-60-mph (97-km/h) sprint. The powertrain's all-around flexibility, high-tech design, respectable efficiency and emotional appeal, makes giving up the keys to this little rocket one of the hardest decisions Ward's 10 Best Engines judges had to make.
BMW AG: 3.0L TURBOCHARGED DOHC I-6
Engine type: 3.0L twin-turbocharged DOHC I-6
Displacement (cc): 2,979
Block/head material: aluminum/aluminum
Bore × stroke (mm): 84 × 89
Horsepower (SAE net): 300 @ 5,800 rpm
Torque: 300 lb.-ft. (407 Nm) @ 1,400-5,000 rpm
Specific output: 100 hp/L
Compression ratio: 10.2:1
Assembly site: Steyr, Austria
Application tested: 135i coupe
EPA city/highway (mpg): 17/25