The new, third-generation, horizontally opposed, "boxer" four-cylinder engine under the hood of the 2011 Subaru Forester may not punch above its weight, pumping out about the same level of hitting power as its predecessor, but it does box smarter.
The "boxer" engine - so called because its pistons jab back and forth on a flat plane like an in-his-prime Sugar Ray Leonard - has been a Subaru staple since it was introduced in one-litre-form in 1966. Which means Subaru has stuck with this unconventional - by mainstream auto industry standards - design for almost half a century now, convinced that both its mechanical and marketing benefits remain worthwhile.
It was introduced in Subaru's first front-drive compact-sized car - the 1000 sedan - and brought benefits of a low centre of gravity, and with the gearbox tucked behind, equal length drive shafts for even torque-steer reducing distribution of its 55 hp. And its configuration - shared with engines from Porsche, Volkswagen and General Motors' Corvair - gave Subaru a unique character that helped differentiate it in a compact car segment in which upright, inline-four-cylinder engines were the norm.
In the years that followed, Subaru also found the flat-engine worked well with the all-wheel-drive systems it was pioneering for passenger cars, technology introduced with the Leone wagon of 1972 and which, some three decades later, became the other star in the Subaru firmament to which it hitched its future.
That first Subie flat-four was a pushrod design that evolved into a single-overhead-camshaft unit in the mid-1980s, which also saw the first application of turbocharging. The second generation, still with single overhead cam heads, was introduced along with the first Legacy in 1989.
For the current remake of this classic engine, Subaru stuck with the basic concept but rethought virtually every aspect from block to heads in search of improved efficiency.
The new naturally aspirated engine (available only in the Forester at the moment) still displaces 2.5 litres, but now has twin-cam cylinder heads with improved intake and exhaust performance and Subaru's Active Valve Control System.
Improved combustion chamber design allows a higher, more efficient compression ratio, the cooling system approach has been revised, internal parts optimized and lightened and lubrication improved, gaining a 30 per cent improvement in frictional losses. It also feels smoother, particularly at idle, and quicker-revving despite a longer piston stroke. But that traditional Subie flat-four growl hasn't completely disappeared.
Performance by the numbers is essentially the same. The new motor matches the 170 hp made by the old one but at 5,800 rpm versus 6,000 rpm and makes 174 lb-ft of torque at 4,100 rpm compared with 170 at 4,400 rpm. Not big changes, but the engine's output is now delivered in a more linear, and thus responsive in more situations fashion, that improves overall drivability.
Fuel economy has been increased in five-speed manual gearbox versions from 10.6 litres/100 km city and 7.5 highway to 9.9 city and 7.4 highway.
Unfortunately, Subaru has had to stick with its old four-speed automatic which just doesn't make the most of this new engine's broader power spread and drivability. Fuel economy ratings with the automatic are improved, from 10.4 city to 9.9 and from 7.7 highway to 7.5, but another gear, or two, would improve this significantly. The test Forester averaged 10.6 litres/100 km after a week that included a lot of four-lane highway driving.
The Forester's power output is competitive in class and more than adequate - it's punchy off the line and will get you up to highway merging speeds safely - but responsiveness would be just that bit better with at least one more gear. New transmissions are apparently in the works.
Other than the engine, little has changed with this popular compact SUV for 2011, just a new grille and some improved materials and a new navi system inside.
The third-generation all-wheel-drive Forester was launched for 2008 and has styling that neatly bridges SUV and crossover territory and provides practical room for four inside a comfortable, eye-pleasing and quiet interior, along with a useful 949 litres of cargo space with the rear seat upright and 1,934 litres with it folded.
Forester pricing starts at $25,995 for a base 2.5x that's equipped with most of the things most of us need. The unit tested was a $29,795, automatic-equipped, 2.5x Touring, which adds a few of the things many of us want, such as 17-inch wheels, a sunroof, power driver's seat and an upgraded audio system.
2011 Subaru Forester Touring
Type: Compact SUV
Base Price: $29,795; as tested, $31,320
Engine: 2.5-litre, DOHC, horizontally opposed four-cylinder
Horsepower/torque: 170 hp/174 lb-ft
Fuel economy (litres/100 km): 9.9 city/7.5 highway; regular gas
Alternatives: Honda CR-V, Toyota RAV4, Ford Escape, Hyundai Tucson, Kia Sportage, Suzuki Grand Vitara, Volkswagen Tiguan