Fuji Heavy Industries Ltd.: 2.5L Turbocharged H-4 Boxer

The last time the Subaru brand won a 10 Best Engines award, in 2004, the list was fueled by testosterone. The rally-ready 300-hp 4-cyl. WRX STI was in good company with similar high-octane entries such as the Audi S4, BMW M3 and two Dodge Ram pickups, one with a heavy-duty diesel strong enough to pull a freight train. The average displacement on the list was 3.5L. Six years later, there is only one

The last time the Subaru brand won a 10 Best Engines award, in 2004, the list was fueled by testosterone.

The rally-ready 300-hp 4-cyl. WRX STI was in good company with similar high-octane entries such as the Audi S4, BMW M3 and two Dodge Ram pickups, one with a heavy-duty diesel strong enough to pull a freight train. The average displacement on the list was 3.5L.

Six years later, there is only one V-8 on the list, no pickups, an average displacement of 2.7L and a subdued tone reflecting new consumer preferences.

The all-new Subaru Legacy GT's 2.5L turbocharged 4-cyl. boxer engine makes this year's 10 Best Engines list because it provides the ideal combination of restrained power and frugal sensibility.

With its horizontally opposed four cylinders churning out 265 hp and a 258 lb.-ft. (350 Nm) torque peak available at 2,000 rpm, the intercooled 2.5L gives the Legacy GT the punch it needs to compete with near-luxury midsize cars.

This engine — in a less edgy state of tune — shares its architecture and many of its specs with the turbocharged 2.5L boxer that took our breath away in the WRX STI six years ago. But judges were equally impressed this year.

By today's standards, the 2004 STI's 2.5L could be perceived as twitchy, raucous and tiresome. Today's market calls for something more practical — yet still fun and technically advanced — and Subaru delivers it in the Legacy GT.

The new iteration has the turbocharger mounted beneath the engine, rather than on top, which is where most turbos reside. The new placement puts the turbo close to the exhaust stream, reducing emissions and turbo lag at low engine speeds.

Subaru has used this approach on a 2.0L diesel engine in Europe, but this is the first gasoline application, as well as the first application in the U.S.

Fuel economy is federally rated at 18/25 mpg (13-9.4 L/100 km) in city/highway driving, but some judges managed better than 28 mpg (8.4 L/100 km).

When power is required while cruising, the turbocharger enables a torque swell that builds to a crescendo from 3,200-5,200 rpm, paying homage to its sporty legacy in the STI. It's a great alternative to the boring family sedan.

FUJI HEAVY INDUSTRIES LTD.: SUBARU 2.5L DOHC H-4 BOXER

Engine type: 2.5L turbocharged DOHC H-4 Boxer

Displacement (cc): 2,457

Block/head material: aluminum/aluminum

Bore × stroke (mm): 99.5 × 79

Horsepower (SAE net): 265 @ 5,600 rpm

Torque: 258 lb.-ft. (350 Nm) @ 2,000-5,200 rpm

Specific output: 106 hp/L

Compression ratio: 8.4:1

Assembly site: Lafayette, IN

Application tested: '10 Subaru Legacy GT

EPA city/highway (mpg): 18/25

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