The Td6 engine powers 90 percent of the Range Rovers sold in Europe, and 50 percent of those sold worldwide. And now it's coming to America.

The Td6 will be available in 2016 model-year Range Rovers and Range Rover Sports (shown in red below), on sale this fall. The diesel models will deliver 32 percent better fuel efficiency than their V-6 gas-engine counterparts, according to Land Rover. Claimed EPA consumption numbers for the diesel Rangies are 22/29/25 mpg city/highway/combined. On the interstates, that means a cruising range of some 650 miles.

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The downsides? Ordering the diesel means paying $1,500 more—the Range Rover Sport Td6 starts at $67,445, and the Range Rover Td6 at $87,445—and living with a slightly slower 0-60-mph time—two-tenths slower in the Sport Td6 and three-tenths slower in the bigger, heavier Range Rover Td6. Neither is enough to warrant a second thought. If you can't afford, or don't want, the supercharged V-8 under the hood of your Range Rover, and you don't do a lot of short trips, this is the engine for you.

Why? There are 440 reasons why. That's the amount of torque, in lb-ft, the Td6 engine grunts out at just 1,750 rpm. By comparison, the gas V-6 makes 332 lb-ft at 3,500 rpm. All that torque at such low revs makes both Range Rovers, already great touring cars, feel effortlessly relaxed on the road, and even more impressively capable off it. Towing capacity is 7,700 pounds.

The Td6 engine was originally designed when Ford owned Jaguar Land Rover, and is made in Ford's Dagenham engine plant just east of London. But it has never been used in a Ford vehicle, and has since been significantly redesigned by JLR engineers. The block is compacted graphite iron, which JLR says has a higher tensile strength than standard gray cast iron, better fatigue strength than aluminum, and added stiffness. Those characteristics mean the block can be relatively light and small, and the deep-skirted, cross-bolted design and one-piece structural aluminum oil pan help absorb combustion noise, improving refinement.

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U.S. customers are not just getting a Euro-spec engine dropped under the hood. Land Rover engineers have covered more than one million miles across more than a dozen states testing the Td6 to ensure it meets U.S. emissions standards and consumer expectations in terms of noise and refinement. During the program Land Rover claims it blind-tested Td6-powered vehicles among customers, and none guessed they were driving something with a diesel under the hood.

That might speak more to the fact that average drivers are perhaps less sensitive to such things than it does to the character of the Td6. If you've spent any serious time behind the wheel of a Range Rover or Range Rover Sport, and pay attention to what the vehicle is doing, you'll know you're driving a diesel. The engine note is different—a soft, muted, oily growl—and there's no mistaking all that torque and the low-rpm shift points.

While not quite as quick from a standing start, there's a liveliness, responsiveness to the midrange rolling acceleration you don't quite get in the Range Rover Sport, or, especially, the larger, heavier Range Rover with the gas V-6. It's creamier, more effortless on the freeway. The Td6-powered cars don't get shift paddles on the steering wheel, but in truth they don't really need them. The eight-speed auto has been nicely calibrated to surf the torque curve; in Sport mode, on a winding road, the transmission downshifted smoothly on the entry into corners, delivering the right gear, right when it was needed.

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Off-road, on Land Rover's rugged Les Comes facility outside Barcelona, the Td6 delivered solid low-speed lugging power, enabling both vehicles to tiptoe through the most challenging terrain. Working in combination with Land Rover's new All-Terrain Progress Control—a sort of off-road cruise control system—it helped make both Range Rovers even more compellingly capable and foolproof in the rough stuff.

Land Rover's V-6 gas engine is not going away—in fact, it gets a 40-hp bump when fitted to the Range Rover HSE for 2016. The U.S. is a very different market from Europe, and U.S. customers have different demands and expectations. But Land Rover has watched how American Audi, Mercedes-Benz, and BMW customers have taken to diesel engines—sales of diesel-powered luxury SUVs have grown 26 percent since 2009—and sees an opportunity. The company expects the Td6 to account for 15 to 20 percent of total Range Rover and Range Rover Sport sales going forward. It's good enough to deserve more.

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The availability of the Td6 turbodiesel engine in the 2016 Range Rover and Range Rover Sport might be the headline news, but all the MY16 Rangies get the following new features and upgrades:

All-Terrain Progress Control

Standard on V-8 models and optional on V-6s, ATPC acts as a low-speed cruise control, operating in low range at speeds of up to 19 mph.