Subaru Forester (2011)

NEW BOXER DIESEL IN DETAIL

Dedicated to the horizontally opposed Boxer engine layout for over 40 years, Subaru engineers were determined to use this proven format for their first diesel engine and for the new, improved version of this powerplant introduced in spring 2011.

The desire was to create a light, compact, strong unit with reduced vibration, noise and internal friction, as well as an ultra-low centre of gravity, compared to an in-line engine. This configuration enhances handling agility and road holding - especially when combined with Subaru's renowned Symmetrical All-Wheel Drive system.

The diesel engine and transmission are not only mounted very low down but also within the vehicle's wheelbase, which further boosts chassis dynamics. The horizontally opposed pistons effectively cancel out any secondary harmonic vibration (vibration with twice the frequency of the engine speed). The crankshaft is short and highly rigid, minimising the vibration noise often present in many other 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 also exceptionally lively and in keeping with Subaru's sporty heritage.

The cylinder block is of a rigid semi-closed deck design, while all five main bearings in the alloy block use metal composite supports for added strength and durability. It also enhances refinement, providing a similar thermal expansion to that of the crankshaft.

A special surface treatment to withstand the diesel engine's high combustion pressures is applied to the high-strength crankshaft, while the uprated cylinder heads have roller rocker arms. In addition, the cam-drive is via a chain system that is better able to handle the variations in torque of the diesel engine.

The new version of the Boxer diesel employs an advanced common-rail fuel-injection system with the fuel highly pressurised before being fed into the common rail. This maximises efficiency, both in terms of power, fuel consumption and emissions.

The development of the revised diesel engine focuses on nine key improvements. These include enhanced turbo-charger efficiency with reduced pumping losses, new exhaust-camshaft timing, increased EGR cooling, optimised flow-rate in the cooling circuit, fitting 4 per cent lighter connecting rods, eliminating the mini-PTC heater and switching to a smaller capacity 150-A alternator.

The new Boxer diesel meets Euro5 emission standards thanks to oxidation catalytic converters and a DPF (diesel particulate filter). This minimises particulate matter - the cause of black smoke.

Performance is improved while fuel economy and emissions are significantly improved. Maximum power is still 147ps at an ultra-low 3,600rpm and the substantial 350Nm (258lb.ft) of torque is now even more accessible, from 1,600 to 2,400rpm - 200rpm lower than previously.

Diesel Subaru Forester's top speed and 0-60mph figure are among the best in the compact SUV class. Top speed is 115.5mph and the sprint to 60mph is dispatched in 10.3 seconds. Even more importantly, in-gear flexibility leaves most competitors trailing thanks to strong mid-range torque and the carefully chosen ratios of the new six-speed manual gearbox.

Fuel economy in the Subaru Forester 2.0D X is improved by an average of 7.2 per cent, to an outstanding 39.8 (urban), 54.3 (extra urban) and 47.9mpg (combined). The Forester 2.0D XC and XS NavPlus derivatives, with their wider tyres, are not far behind at 39.2 (urban), 53.3 (extra urban) and 47.1mpg (combined). The new CO2 emission figures are especially impressive, down from 167 and 170g/km, respectively to just 155 and 158g/km.

To maximise the benefits of this new-found frugality, the Boxer diesel's fuel tank is larger - 64 litres compared to the petrol model's 60 litres, giving it a range of 625miles / 1,000km.

2.0-LITRE PETROL IN DETAIL

The latest Subaru Boxer petrol engine delivers improved environmental credentials compared to its predecessor, while also affording smooth acceleration. The new FB-A engine (found in the 2.0 X and XS Forester models) offers stronger low and mid-range pulling power, enhanced flexibility and improved fuel economy, as well as lower exhaust emissions.

The 2.0-litre four-cam configuration remains the same, featuring twin overhead camshafts per bank (DOHC), four valves per cylinder and an Active Valve Control System (AVCS) - a form of variable valve timing. The stroke has been increased by an additional 8mm to 92mm, offering an improvement in torque in the low- and mid-speed ranges, in addition to reduced emissions. Capacity is now 1,995cc.

The cylinder head, cylinder block and valve train have been re-designed, while the intake and exhaust systems have been extensively re-worked to optimise efficiency through increased air flow. Modifications to the cooling system channels now allow the engine to reach operating temperature quicker, with faster increases in oil temperature, reducing friction and improving fuel economy.

For this third-generation Boxer petrol engine, Subaru also employs a chain-type camshaft drive, as found on Subaru's six-cylinder engines and the brand's Boxer diesel engines. A more compact design and maintenance-free setup are two important benefits of this alteration.

Urban / extra urban / combined fuel consumption figures are now 29.1 / 44.8 / 37.7mpg for the Subaru Forester 2.0 X and XS automatic models, with an improved CO2 figure of 174g/km. This compares favourably with the petrol automatic competition.

The four-speed automatic achieves the 0-60mph dash in 12.3 seconds, with a maximum speed of 115mph, while improved torque allows higher gearing for improved refinement and economy, with no sacrifice in engine response.

Manual versions of the Forester show similar improvements with urban / extra urban / combined figures of 30.1 / 44.1 / 37.7mpg, and a low CO2 rating of 173g/km. Top speed for the manual Subaru Forester is 114mph with a 0-60mph time of 10.6 seconds.

TRANSMISSION

The Forester diesel boasts a six-speed manual gearbox with optimised ratios for quiet, refined high-speed cruising and flexible low-speed manoeuvres. For example, sixth gear is slightly higher than fifth on the Legacy and Outback boxer diesels, with a ratio of 0.557:1, delivering 31.5mph / 1,000rpm for the Subaru Forester 2.0D X, while first gear is lower at 3.454:1.

The six-speed manual gearbox employs a cable change. Apart from giving a consistent feel, cables isolate transmission and engine vibration, enhancing refinement.

Petrol models are also available with a four-speed automatic transmission. This provides smoother changes with greater sensitivity to the driver's wishes. It is more efficient, saving fuel, because a slip lock-up device reduces wasted engine revs. In addition, advanced electronics - linked to an electronic throttle - match engine speed with the best gear for any given situation.

A new feature is 'Sports Shift' which allows drivers to select from 'normal', 'sports' or 'manual' modes, allowing them to 'tap-shift' between the gears at will.

As with previous models, the full-time All-Wheel-Drive transmission features a 60 / 40 Active Torque-Split on the automatic. However, the split varies according to changing road surface and weather conditions.

SYMMETRICAL ALL-WHEEL-DRIVE

All Forester models enjoy the benefits of Subaru's acclaimed full-time Symmetrical All-Wheel-Drive system, as well as Subaru Vehicle Dynamics Control, as standard. The latter system uses sophisticated sensors to detect side-to-side and front-to- rear slip, plus sudden steering movements. It controls oversteer / understeer and potential loss of control by braking individual wheels and cutting engine revs - all in a matter of milliseconds.

The Subaru Forester's quick-thinking full-time Symmetrical AWD system splits power 50 / 50 per cent front / rear as its default setting. However, as soon as slip is detected, the centre differential with its viscous-coupling distributes torque to the axle with the most grip.

RIDE AND HANDLING

A sophisticated Symmetrical All-Wheel-Drive system, low-friction, long-travel four-wheel independent suspension and low-centre-of-gravity Boxer engine, all contribute to the Subaru Forester's reputation for outstanding chassis dynamics.

It offers a highly absorbent ride with precise geometry control for accurate straight-line running over uneven road surfaces backed by extremely responsive steering and handling.

The rear multi-link, double-wishbone suspension liberates more luggage space thanks to its compactness compared to the previous rear-strut arrangement. And because it is attached to a sub-frame via bushes, with the mounting section moved to under the floor itself, road noise is reduced, too.

To boost ride comfort, the rear springs and shock-absorbers are mounted behind the centre-line of the rear wheels, with the wheel stroke itself moving rearwards. A rear anti-roll bar is standard.

Like all previous Subaru Forester incarnations, the rear suspension features self-levelling which aids stability when laden and ensures a constant ground clearance - now a substantial 215mm - 10mm greater than before.

At the front, the previous sub-frame has been eliminated, saving 20kg in weight. However, a new box-section for the front cross-member provides the same level of structural rigidity.

The MacPherson strut suspension and anti-roll bar layout is based on that used by the highly acclaimed Legacy and Impreza. It offers high lateral rigidity which improves steering response and cornering stability.

This is further enhanced by an especially rigid mounting for the steering rack and the positioning of the steering gearbox and electric motor below the rack for a more consistent feel. Furthermore, special suspension bushes and attachment points reduce road shock.

A more linear feel to the steering has been achieved, while the steering gear ratio has been changed for a sportier feel and the rack diameter is increased from 23 to 26mm.

For the Boxer diesel Subaru Forester, the front damping has been firmed up together with the steering to sharpen handling and compensate for the 45kg increase in engine weight.

Wheel and tyre sizes have been optimised for the new Subaru Forester's chassis and anticipated all-terrain use.

The Subaru Forester X models feature 16 x 6.5-inch alloy wheels with 215/65 R 16 tyres, while Forester XC, XS and XS NavPlus have 17 x 7.0-inch alloy wheels with 225/55 R 17 tyres.

PASSENGER AND PEDESTRIAN PROTECTION

Both occupants and pedestrians are well protected by the Subaru Forester thanks to a whole series of safety measures aimed at achieving the highest standards.

Curtain and side airbags are now fitted to all models together with driver and front passenger dual-stage airbags. The front seatbelts have pre-tensioners, anti-whiplash front head restraints are standard and the front seats have energy-absorbing backs.

The brake pedal is energy-absorbing, being designed to snap away under severe impact, protecting the driver's lower limbs. In the rear seat, two ISOFIX-compatible child seat mountings are fitted.

Also fitted as standard, the anti-lock braking system (ABS) comes with electronic brakeforce distribution (EBD). This system juggles the braking force between front and rear wheels according to weight transfer during deceleration. Unlike the previous model, the new Forester has ventilated front disc brakes.

High-tensile steel is used extensively throughout the bodyshell, providing good 'crushability' where needed for protecting the passenger area. Not only does the elimination of the previous Subaru Forester's front sub-frame reduce weight by 20kg, but the new structure better dissipates front impact forces.

Pedestrian protection is also greatly enhanced. Because the Subaru Forester is higher than a car, more space has been made between the bonnet and catch, while the bonnet itself has been designed to spread impact load over its entire surface. The back of the bonnet compresses easily and the cowl ahead of the windscreen is designed to dissipate collision energy.

A shock-absorbing plate has been installed ahead of the front bumper beam to reduce pedestrian leg injuries. This design meets European pedestrian safety regulations while retaining the Subaru Forester's off-road approach angle, as expected of an SUV.

WARRANTY

All Foresters come with the reassurance of a three-year or 60,000-mile warranty plus 12-year anti-corrosion cover and three-year paintwork warranty.

This is in addition to three years membership of Subaru Assistance - a comprehensive home and roadside repair and recovery package throughout the UK and Europe, administered by Mondial Assistance.

Service intervals are 12,000 miles or one year - whichever arrives first.

Insurance ratings are also extremely competitive at Group 9E for the Subaru Forester 2.0D X and XC and Group 10E for the Subaru Forester 2.0D XS NavPlus.