Ford Motor Co.'s 2.5L DOHC I-4 HEV: Great Fuel Economy

Placing a hybrid-electric vehicle on the 10 Best Engines list is always a charged affair.

Only three auto makers have managed to crack the list this decade, amid questions from internal-combustion purists who want this competition to be only about engines, not tag-team systems that need electric motors.

This year, a fourth OEM joins that short list as Ford Motor Co. collects a trophy for its second-generation Escape Hybrid cross/utility vehicle, which benefits in no small measure from Ford's all-new 2.5L DOHC I-4. The engine replaces the less capable 2.3L I-4 in the first-generation HEV.

With intake variable camshaft timing, the new 4-cyl. delivers a broader power band and operates on the Atkinson combustion cycle (similar to most other hybrids), which improves efficiency up to 10% over conventional Otto-cycle configurations by keeping the intake valves open longer.

This reduces the engine's pumping losses by allowing a small portion of the fuel/air charge to flow back into the intake.

Mechanical changes include new intake and exhaust manifolds; a new intake camshaft; and higher-compression pistons (12.3:1) vs. the non-hybrid I-4 (9.7:1).

Engine type: 2.5L DOHC I-4

Displacement (cc): 2,488

Block/head material: aluminum/aluminum

Bore × stroke (mm): 89 × 100

Horsepower (SAE net): 155 @ 6,000 rpm

Torque: 136 lb.-ft. (184 Nm) @ 4,500 rpm

Specific output: 61 hp/L

Compression ratio: 12.3:1

Electric motor: 71 kW (94 hp) @ 5,000 rpm, 330-volt NiMH battery

Assembly site: Chihuahua, Mexico

Application tested: Ford Escape Hybrid FWD

EPA city/highway (mpg): 34/31