Subaru has launched its first diesel-powered cars with a world-first two-litre horizontally-opposed engine.
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The new engine is initially only for Europe and offered only in the Legacy Sports Tourer and Outback crossover models.
“Saloon versions may follow once supplies become more plentiful,” Subaru’s UK importer said.
The redesigned Forester will have the diesel option from launch next September and it will also go into the Impreza three months later.
Subaru’s first diesel engine was developed in-house using, the automaker said, over 40 years’ expertise in ‘boxer’ engine technology coupled with turbocharging know-how gleaned from world rally championship participation.
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By GlobalDataSubaru (UK) managing director Lawrence Good, said: “The significance of this outstanding new diesel engine to both sales opportunities and our dealer network cannot be underestimated.
“With a UK diesel market share now running at 40% this is the answer to many loyal and potential customers’ future motoring needs.”
The new diesel develops 150PS of power at 3,600 rpm and 258 lb ft torque at 1,800 rpm.
Subaru said its engineers were determined to use the ‘boxer’ format for their first diesel engine.
The reasons were to create a light, compact, strong unit with reduced vibration, noise and internal friction compared to an in-line engine and for a low centre of gravity said to enhance handling agility and roadholding.
Subaru claims class-leading light weight with the horizontally-opposed pistons effectively cancelling out the secondary harmonic vibration.
The crankshaft is short and highly rigid, minimising the vibrational noise of many diesel engines.
The superior balance of the horizontally-opposed engine means internal rotational inertia and friction are drastically reduced compared with an in-line engine.
Compared to the two-litre petrol engine fitted to the Impreza, Legacy and Forester, the Boxer diesel has a longer stroke and 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 petrol’s 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 engine has a common-rail fuel-injection system with the fuel being pressurised at 180MPa.
Special, short-length solenoid injectors ensure the engine’s width is no greater than that of the petrol 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 centre-of gravity position under the engine and close to the catalytic converters increases environmental performance.
The Boxer Diesel meets Euro4 emission standards thanks to oxidation catalytic converters, a particulate filter and exhaust gas recirculation.
Top speed for the Legacy 2.0TD R Sports Tourer is 126mph with a 0-60 mph time of 8.5 seconds.
Fuel economy is 39.8/56.5 and 49.6 mpg on the EC combined cycle with CO2 emissions of 151g/km.
Changes to accommodate the diesel engine include liquid engine mounts, extra sound-proofing and higher ratios in the five-speed manual gearbox to suit the diesel’s stronger torque and lower engine speed.
The power-steering is now electric to improve fuel economy while front spring rates have been re-tuned to suit both the diesel engine and new steering system.
The diesel also has uprated front brakes and reduced gear-lever movement.
The air-conditioning unit has been modified to provide hot air earlier in the engine’s warm-up cycle.
Visual changes distinguishing the diesel models include new cloth seat trim and a bonnet air scoop.
