Check to see if pigs are flying. That's what we figured would happen before any 3-ton GMC Yukon SUV achieved 20 mpg (11.8 L/100 km) in city driving.

Yet that's the powertrain near-miracle delivered by General Motors Corp.'s all-new 2-Mode hybrid-electric system, essentially an electronic continuously variable transmission (CVT) augmented by two electric motors, fixed-gear capability and a highly optimized, 6.0L variant of GM's small-block V-8. The breakthrough, of course, is that city economy of 20 mpg - 21 mpg (11.2 L/100 km) for 2-wheel-drive models — is a 50% leap over the same vehicle powered only by a 5.3L V-8.

GM boasts the Yukon Hybrid is as efficient in city driving as a 4-cyl. Toyota Camry. GM believes hybrid-electric vehicle technology, initially at least, is best suited for the thirstiest vehicles, where efficiency enhancements make the most impact. The 2-Mode is a significant achievement.

ENGINE SPECS

Engine type: 6.0L OHV 90° V-8

Displacement (cc): 5,967

Block/head material: aluminum/aluminum

Bore × stroke (mm): 101.6 × 92.0

Horsepower (SAE net): 332 @ 5,100 rpm

Torque: 367 lb.-ft. (498 Nm) @ 4,100 rpm

Specific output: 55 hp/L

Compression ratio: 10.8:1

Electric motor/transmission: (2) 60-kW electric motors/300-volt NiMH battery pack (30 hp electric boost)

Assembly site (engine/transmission): Silao, Mexico/Baltimore, Maryland

Application tested: GMC Yukon Hybrid 4WD

Fuel economy, city/highway (mpg): 20/20