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
