Subaru open doors with new diesel ‘boxer’ engine

Having honed the horizontally opposed engine over the last 40 years, it made sense for Subaru to retain the layout for what is known as the world's first diesel boxer engine.

With pairs of opposing pistons, it's a layout that is said to cancel out secondary harmonic vibrations, leading to an ultra-smooth package. And having spent a week behind the wheel of a Legacy Sports Tourer, FG is inclined to agree.

It is a sweet, free revving two-litre that is so hushed and keen, you would be hard pressed to tell it is a diesel. It revs and sounds like a petrol with a fine pedigree, but easily gave 44mpg back.

Inside the car, it is serene, with only the occasional mild shake filtering through at idle. Though there are reminders you are powered by an oil burner – a somewhat pointless economy gauge beneath the rev counter attempts to massage your eco-side by reminding you that you are driving something frugal, and the word ‘diesel' is clearly stamped on the fuel gauge too. Though the latter could be a saving grace for long-standing Subaru customers that have just made the switch from petrol versions.

Bystanders however, won't suffer from the same curiosity – outside, it rattles and clatters at idle just like any other modern diesel engine.

With 150hp developed at 3,600rpm and 350Nm of torque found at 1,800rpm, there is plenty of muscle to propel the Legacy Sports Tourer along at a fair lick. It pulls effortlessly and develops a sweet note when revved, which gives the impression it is just getting into its stride when full power arrives and it's time to grab another gear.

But there is a drawback here – there are only five speeds in the Legacy's box. They are perhaps a bit leggy too, and this car would certainly benefit from six closer speeds, as found in the Forester.

Subaru's torque delivery feels optimistic. And we suspect it falls off pretty suddenly below the suggested 1,800rpm peak – more than once did it catch me out with countless mis-judged rolling starts in second gear. It just won't go from idle and needs a good helping of revs, which often forced me to plump for first gear when you know perhaps that second gear should handle the mission.

That said, it is still a great engine and you know that when the second-generation diesel eventually arrives, it will be lot better too. We've got our fingers crossed that a flat-six diesel might join the range too.

With such a practical estate car backed up by a sure-footed full-time four-wheel drive system, we believe Subaru's fortunes could be about to climb. And those who need a bit more ground clearance can find the same power unit in the Legacy Outback.