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January 30, 2008
Driving the World’s First Boxer Diesel
Both conceal turbocharged power and 4wd, but which is the better drive, Mazda 6 MPS or Subaru Impreza WRX STI Spec D?
Source: Edmunds
By Alistair Weaver
We’re driving the 2008 Subaru Legacy Boxer Diesel in Malaga, Spain, but we might as well be in Southern California.
Everything looks like Southern California already, right down to the Spanish on the street signs. And while you might think of the distinctive clatter of diesel from beneath the Legacy’s hood as the signature sound of European traffic these days, we promise you that it will be heard on the streets of Orange County soon enough.
This 2008 Subaru Legacy Boxer Diesel is a European model meant to go on sale this spring, but we think it’s surely coming to America. A wave of diesel technology is headed toward the United States, and Subaru clearly wants to be riding the crest.
10 Years in the Making
Kenichi Yamamoto, the man in charge of the development of this car, makes no secret of Subaru’s lofty ambitions for the 2008 Subaru Legacy Boxer Diesel, which features the world’s first horizontally opposed diesel engine for passenger cars.
"The benchmark cars were the BMW 320d, the Audi A4 and the Honda Accord turbodiesel," he says. Yamamoto admits that research started on the project nine years ago, but it was impossible at that stage to build a business case for the engine. "Now the situation is different," he notes. "In Europe we need to reduce our carbon-dioxide emissions; we cannot survive without diesel."
The new engine was given the green light for production just two years ago, prompting an engineering scramble to turn a promising concept into a reality. It was a tough challenge, but Subaru has not skimped on the technology.
Practical Reengineering
The basic lump is familiar, a turbocharged, DOHC 1,998cc horizontally opposed four-cylinder engine. To convert this architecture to diesel, the first significant change is a dramatic 6mm reduction in the cylinder bore and an 11mm increase in the length of the stroke. Now the bore and stroke are symmetrical at 86.0mm. One of the results is a much shorter crankshaft that measures 13.9 inches, some 2.4 inches shorter than before.
To minimize weight, the block as well as the cylinder heads are made from aluminum. Subaru tells us that the structural integrity of the boxer configuration helps make this measure possible. As with almost every European turbodiesel, the Subaru employs common-rail technology for the new engine. The turbocharger is mounted below the engine and connected directly to the catalytic converter, an installation that’s becoming more common in all kinds of engines because it promotes quicker light-off for the catalyst.
The power figures are impressive. The boxer diesel produces 148 horsepower at 3,600 rpm and 258 pound-feet of torque at just 1,800 rpm. The engine is capable of 60.5 mpg. This compares with the 320d’s turbocharged 2.0-liter inline-4 diesel that produces 174 hp and 271 lb-ft of torque, while the Honda Accord’s turbocharged, 2.2-liter inline-4 diesel delivers 138 hp and 251 lb-ft of torque. Meanwhile, the gasoline version of Subaru’s 2.0-liter four-cylinder boxer also manages 148 hp, but just 144 lb-ft of torque.
Driving in the Real World
The new engine will appear first in the 2008 Subaru Legacy Boxer Diesel and the 2008 Subaru Outback Boxer Diesel, both of which are scheduled to be introduced in Europe this spring. The badge on the Legacy sedan’s trunk reads, "Boxer Diesel" and the car is also set apart by the scoop on the hood that directs air to the air-to-air intercooler on top of the engine. Prod the starter button and you’ll hear an unmistakable diesel rattle. It’s not loud or especially intrusive, but it’s there all the same.
Move away and the rattle subsides immediately. Subaru has increased the quantity of acoustic insulation in this car, but there can still be no denying that this is an exceptionally (and unexpectedly) quiet engine, an aspect of the horizontally opposed configuration, Subaru claims. At full throttle, you can hear the characteristic growl of a Subaru boxer, although it’s deeper than the gasoline equivalent. Really, you have to listen hard for it, and the engine noise at highway speed is notable only by its absence.
The engine pulls cleanly and easily from as low as 1,700 rpm, although its best work is done by the time the tach needle reaches 4,000 rpm. The power flexibility through the midrange is impressive. In top gear, the diesel takes 23.4 seconds to accelerate from 50 to 100 mph, a veritable sprint compared with the 37.0 seconds it takes a Legacy with a normally aspirated 2.0-liter gasoline engine to accomplish the same feat.
Our only criticism of the Legacy Boxer Diesel has to do with the transmission. First, the shift lever is farther forward than before. But more important, the wide-ratio five-speed doesn’t seem to make the best use of the wide power band, and surprisingly enough a six-speed would be a better match. Yamamoto admits that a six-speeder is under development and will be ready by the end of the year, together with an automatic version.
The Business Case for Diesel
At present, Subaru’s new diesel engine is destined only for Europe, but Subaru is taking a wait-and-see approach to its introduction in Japan and the U.S. At present, the engine will not meet California’s stringent air emissions regulations. "We would only introduce the car in the U.S. if it was legal in every state," says Yamamoto. "Meeting the California legislation is very hard and very expensive. We are researching it, but there is no timetable." Subaru estimates that fitting the particulate filter needed to make the engine fully compliant would add around $1,500 to the price of the car.
Nevertheless, Hirofumi Senoo, the general manager of Subaru’s European test center tells us, "Diesel is the main focus for the U.S. market. It has more potential than hybrid gasoline engines because hybrids are only good for the city." Subaru will let others take the lead in the introduction of diesel to the U.S., but will be ready to strike if the market becomes receptive.
Only the Beginning
This engine is really only the start of Subaru’s diesel strategy. In addition to the 2008 Legacy Boxer Diesel and 2008 Outback Boxer Diesel, the Impreza will feature the new engine toward the end of the year.
And, having proven the technology, Subaru is confident that it can produce versions with as much as 161 hp without any risk to its durability, although such a power output would increase fuel consumption and air emissions. There is even talk of an STI version or even a rally special. "It is my personal opinion that it would be good to see a motorsport version," Senoo says. "A WRC engine has lots of torque but not much power."
Europe has been deluged with a wide range of brilliant turbodiesels in recent years. BMW in particular has led the way with the development of diesels that are quieter, more frugal, less polluting and, in most cases, more powerful than their gasoline equivalents. Subaru is late to the party but its entrance is impressive.
Once on the move, this is one of the most refined diesels on the market today. This is a boxer that can punch above its weight.
Source: Edmunds
By Alistair Weaver
Technorati Tags: subaru, legacy, subaru legacy, diesel boxer, diesel subaru, diesel legacy, subaru legacy diesel
- Posted in : 2008 Subaru, Articles, Road Tests
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