Subaru has chosen the British International Motor Show (July 23 to August 3, ExCeL, London) to unveil the Saloon version of its critically acclaimed new Boxer Diesel Legacy.
Launched earlier in the year in the Legacy Sports Tourer and Outback, the world’s first boxer-diesel-engine for a passenger car offers outstanding refinement, throttle response and fuel economy coupled with class-leading ultra-low emissions.
Also exceptional is the new Boxer Diesel Legacy’s handling thanks to the engine’s light weight and low center-of-gravity afforded by its horizontally-opposed cylinder layout.
The new Saloon is priced from £19,995 on-the-road and is available in the three trim levels of 2.0D R, 2.0D RE and 2.0D REn. It joins the Subaru Legacy Sports Tourer and Outback crossover mid-sized estates which were launched this February.
This is Subaru’s first diesel engine – developed in-house using over 40 years’ expertise in ‘boxer’ engine technology coupled with turbocharging know-how gleaned from the fierce World Rally Championship arena.
Class-Leading Figures
The 150 PS Boxer Diesel Legacy Saloon boasts the best fuel efficiency in the 4WD passenger car class – and the lowest exhaust emissions.
In fact, the new Legacy 2.0D Saloon returns 50.4 mpg on the Combined Cycle with only 148 g/km of CO2.
Nor are these figures achieved at the expense of performance. The Boxer Diesel Legacy Saloon has a 129 mph top speed and 0-60 mph time of only 8.3 seconds.
Refinement is also a Boxer Diesel strongpoint, with official moving sound levels of 70.5 dB (A). Even a Rolls-Royce Phantom is higher at 72.0 dB (A).
Thoroughly-Developed Package
The new Boxer Diesel Legacy Saloon is a thoroughly-developed model in its own right with several unique features to suit its diesel application.
For example, 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 carefully 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.
Even 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 petrol powerplants.
Visual changes include new cloth seat trim for the Legacy Saloon 2.0D R and a discreet bonnet air intake scoop.
Boxer Diesel Secrets Explained
-Exceptionally compact, light and strong
-Low friction ‘Boxer’ balance cancels out vibration
-Flat four’s low center-of-gravity boosts handling agility
-Punchy throttle response
-Common-rail fuel-injection for greater efficiency
-Solenoid injectors for compactness
-Variable-vane turbocharger mounted under engine for low center-of-gravity
-Highly efficient, fast-warm catalytic converter also mounted under engine
Dedicated to the horizontally-opposed ‘boxer’ engine layout for over 40 years, Subaru engineers were determined to use this 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 an ultra-low center-of gravity.
This enhances handling agility and roadholding – especially when combined with Subaru’s renowned symmetrical all-wheel drive system.
In fact, the entire engine and transmission are not only mounted very low down but also within the wheelbase which further boosts chassis dynamics.
Cancelled Out Vibration
The 2.0 liter Boxer Diesel has a class-leading light weight with the horizontally-opposed pistons effectively canceling out the secondary harmonic vibration (vibration with twice the frequencies of the engine speed).
The crankshaft is short and highly rigid, minimising the vibrational noise of many diesel engines.
And the superior balance of the horizontally-opposed engine means internal rotational inertia and friction are drastically reduced compared with an in-line engine.
Reduced internal friction means throttle response is exceptionally lively and in keeping with Subaru’s sporty heritage.
Compared to Subaru’s 2.0 liter petrol 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.
Even More Compact
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 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.
Advanced Fuel-Injection And Turbocharger
The new Boxer Diesel uses an advanced common-rail fuel-injection system with the fuel being pressurised at 180 MPa before being fed into the common rail. This maximises efficiency, both in terms of power, fuel consumption and emissions.
Special, short-length solenoid injectors ensure the engine’s width is no greater than that of the 2.0 liter ‘boxer’ 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 center-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. It is the most environmentally-friendly vehicle in the AWD passenger car class.
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