Subaru Forester has new petrol and diesel flat-four engines

Subaru's biggest-selling UK model, the Forester crossover, has just been treated to new petrol and diesel engines to improve efficiency and reduce running costs.

The new petrol motor is the 2.0-litre FB series, still a flat-four like the engine it replaces but an all-new design. Unlike previous engines with a square bore/stroke ratio, the FB is a long-stroke design and it has two chain-driven overhead cams on each bank of cylinders, with AVCS variable valve timing on intake and exhaust valves. According to Subaru the FB is substantially more economical than its predecessor, generates less CO2, and has been designed for greater low-speed pulling power.

Subaru FB petrol engine in the Forester

FB engine is the first all-new flat-four from Subaru since 1989, has long-stroke design.

Despite that last claim the FB is still an engine that needs to be worked hard, giving its best between 3500rpm and the red line at 6600. You have to make the most of the gearbox - a manual with five speeds, which isn't many by today's standards - to keep the motor spinning, but the flat-four starts to sound raucous if you venture anywhere near the limit.

As an alternative to the petrol engine Subaru offers a revised version of the 2.0-litre Boxer diesel which has slightly less power but a great deal more torque (145bhp/258lbft versus 148bhp/145lbft). The diesel pulls convincingly from 1750rpm all the way to its 4700rpm limit, and remains smooth and quiet throughout the rev range. The bulging torque curve makes the diesel Forester convincingly quicker than its petrol brother on the road, and it's easier and more relaxing to drive, too.

Subaru Forester interior

Forester interior shares much with Impreza. Steering is light and direct.

The rest of the Forester is much as it was before. The interior is much like that of the Impreza. Light, direct steering and a high driving position coupled to good visibility makes it feels small and wieldy on the road, as happy winding along a country lane as it is navigating the urban jungle. In town or out of it the supple suspension and 55-series tyres smoothe out the worst of rippled and pot-holed roads. All models come with automatic self-levelling at the rear to keep the Forester level even when carrying a heavy load, or towing a nose-heavy trailer. That and the permanent four-wheel drive system should make this a very effective tow car, particularly with the torque-rich diesel engine.

The Forester is a useful machine if you need an all-weather vehicle capable of carrying (or towing) a good-sized load. The new engines - which are due to appear in other Subaru models from next year - make significant improvements on the motors they replace. Though the Boxer diesel comes at a £1700 premium, it's the more effective power unit of the pair by quite a margin.