Special Report

Ward’s 10 Best Engines

It’s tragic to think the U.S. market, having just gotten a taste of contemporary, European-style, torque-rich clean diesel engines, could see them disappearing in the future, the victim of extremist emissions regulations proposed in California.

The debate is ongoing, and reasonable voices for auto makers such as BMW AG still have a good shot at convincing the California Air Resources Board that fuel-efficient diesels can play a vital role in scaling back carbon-dioxide tailpipe emissions.

The best way to win the argument is to send these environmental autocrats for a daylong drive along the Pacific Coast Highway in the BMW 335d. They will return with smiles on their faces and a firm grasp of the enthusiast culture that embraces diesel as the perfect balance between performance and fuel efficiency.

For achieving this balance so well, BMW wins its second consecutive 10 Best Engines award for its outstanding 3.0L DOHC inline-6 turbodiesel.

It dazzled the Ward’s judges with its quiet deportment at steady-state cruising, thunderous power delivery when required and smoke-free emissions all the time.

Mitigating turbo lag is the unique 2-stage induction strategy that allows a small turbocharger to spool up quickly for low-end response, which triggers a larger compressor to force even more air into the combustion chamber, picking up the slack at higher engine speeds.

This state-of-the-art all-aluminum I-6 relies on high-pressure common-rail fuel delivery, piezoelectric injectors and a raft of exhaust aftertreatment systems to remove diesel particulates, oxides of nitrogen and other emissions, allowing the 335d and the X5 xDrive35d SUV to be sold in all 50 states with the same engine.

An onboard AdBlue system injects small amounts of a water/urea solution into the exhaust from two onboard tanks. The tanks and respective lines are heated to prevent freezing, and they normally need to be refilled only during scheduled maintenance.

Stir all this technology together, and the result is a thrilling European sport sedan rated by the Environmental Protection Agency at 23/36 mpg (10.2-6.5 L/100 km) in city/highway driving, while stomping its way to 60 mph (97 km/h) in 6.0 seconds. It’s the fastest diesel passenger car available in the U.S.

Several Ward’s editors managed to get about 30 mpg (7.8 L/100 km) driving the 335d.

There’s nothing shabby about those numbers, or the 26 mpg (9 L/100 km) highway rating for the 5- or 7-passenger diesel X5, which can sprint to 60 mph in 6.9 seconds.

Specific output of 88 hp/L previously was unheard of for a diesel, but BMW already trumps that number with the 102 hp/L delivered by the 2.0L twin-turbo diesel I-4 in the 123d available in Europe. The auto maker officially hasn’t announced that engine is headed for U.S. shores, but the hints have been unmistakable.

For the meantime, we can revel in the glory of the 335d, the gift that keeps on giving, even in California.

tmurphy@wardsauto.com

Ward's 10 Best Engines is a copyright of Penton Media Inc. Commercial references to the program and/or awards are prohibited without prior permission of Ward's Automotive Group.