Subaru has just completed the first thorough overhaul of its petrol boxer engines in 21 years.
Although the engine has been updated since it was introduced in the orginal Legacy in 1989, this is the first time the company has gone back to the basic structure for a more significant renewal.
The result is a 10% improvement in economy for the 2.0-litre version which, Subaru says, continues to develop 146bhp. No power output for the 2.5-litre has been given, but the current engine provides 165bhp.
The new engine design is more flexible and will allow the boxer layout to meet future emissions regulations with adaptations.
Subaru likes the unusual layout, in which the horizontally opposed pistons punch out like two boxers standing back-to-back, because it says it cuts vibration and gives the car a lower centre of gravity.
The Forester will be the first car to benefit from the more efficient engines later in the year.