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Subaru’s First Boxer Diesel Passenger Cars: Legacy Sports Tourer and Outback
21 January 2008
|Boxer Diesel Outback 2.0 TD.|
The turbocharged 2.0-liter horizontally-opposed diesel engine develops 110 kW (148 hp) of power at 3,600 rpm and 350 Nm (258 lb-ft) of torque at 1,800 rpm, and is coupled with Subaru’s symmetrical all-wheel drive system. The Boxer Diesel meets Euro 4 emission standards with oxidation catalytic converters, a particulate filter and exhaust gas recirculation.
The most fuel efficient of the models, the Legacy Sports Tourer 2.0TD R, consumes 5.7 L/100km (41.3 mpg US) on the European combined cycle with 151 g/km of CO2. The Legacy Sports Tourer has a 126 mph top speed and 0-60 mph time of 8.5 seconds while the Outback (with fuel consumption of 5.8 L/100km, or 40.6 mpg US) is only slightly behind at 124 mph and 8.8 seconds for the 0-60 mph dash.
The new Boxer Diesel Legacy and Outback feature several unique features to suit their diesel application.
The engine has liquid mounts, with the body benefiting from extra sound-proofing to enhance refinement, while the five-speed manual gearbox has higher ratios to suit the diesel’s stronger torque and lower engine speed.
The power-steering is now electric to improve fuel economy and tuned for strong feel and response. Front spring rates have also been tuned to suit both the diesel engine and new steering system.
The Boxer Diesel’s front brakes have also been uprated and the gear-lever length reduced by 10 mm for a sportier, shorter throw.
The air-conditioning unit has been modified to provide hot air earlier in the engine’s warm-up cycle, diesel engines having different characteristics to gasoline powerplants.
|The boxer turbo diesel. Click to enlarge.|
Use of the horizontally-opposed boxer engine layout enabled the creation of a light, compact, strong unit with reduced vibration, noise and internal friction compared to an in-line engine and for an ultra-low center-of gravity. The entire engine and transmission are not only mounted very low down but also within the wheelbase, further boosting chassis dynamics.
The 2.0-liter Boxer Diesel has a class-leading light weight with the horizontally-opposed pistons effectively cancelling out the secondary harmonic vibration.
The crankshaft is short and highly rigid, minimizing the vibrational noise of many diesel engines. The superior balance of the horizontally-opposed engine means internal rotational inertia and friction are reduced compared with an in-line engine.
The engine has a ‘square’ bore and stroke of 86 mm and a compression ratio of 16.3:1. Compared to Subaru’s 2.0-liter gasoline engine fitted to the Impreza, Legacy and Forester, the 2.0-liter Boxer Diesel has a 11 mm longer stroke and 6 mm smaller bore for a capacity of 1,998 cc versus 1,994 cc.
Thanks to a bore pitch shortened from 113 mm to 98.4 mm, the overall engine block length is only 353.5 mm compared to the gasoline version’s already compact 414.8 mm.
The block is of a rigid semi-closed deck design, while all five main bearings in the alloy cylinder block use metal composite supports for added strength and durability. It also enhances refinement, providing a similar thermal expansion to that of the crankshaft.
Extra water-cooling slits have been added between the cylinder bores and the high-strength pistons are squirted with oil to enhance cooling. The large ends of the connecting rods feature an asymmetrical profile for assembly precision and reduced friction.
The high-strength crankshaft has a special surface treatment to withstand the diesel engine’s high combustion pressures while the uprated cylinder heads have roller rocker arms. In addition, the cam-drive is via a chain system that better handles the variations in torque of a diesel engine.
The new Boxer Diesel uses an advanced 180 MPa (1,800 bar) common-rail fuel-injection system. Special, short-length solenoid injectors ensure the engine’s width is no greater than that of the 2.0 litre boxer gasoline unit, despite the diesel’s longer piston stroke.
The variable nozzle turbocharger ensures the correct boost throughout the engine’s rev-range and its low center-of gravity position under the engine and close to the catalytic converters increases environmental performance.
The Boxer Diesel engine will initially only be fitted to European-market cars, with the yet-to-be introduced new Forester receiving the engine in September and new Impreza three months later.
On sale from February 2008, the Subaru Legacy Sports Tourer and Outback crossover mid-sized are priced from £19,995 (US$38,800) for the Legacy 2.0 TD R model.
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