Subaru's Boxer Diesel

Fuji Heavy Industries Ltd. uses the recent Geneva auto show to unwrap its highly anticipated Subaru flat-4 diesel engine, marking the first time the auto maker has had a compression-ignition powerplant in its stable.

Planned for a formal launch sometime next year, the all-new H-4 engine is set to boost Subaru's market share in Europe, where nearly half of car sales are oil-burners.

The first model to feature the turbodiesel is expected to be on the Legacy platform and unveiled at the Frankfurt auto show in September.

Advantages of the “boxer” layout are inherent rotational balance, negating a balancer shaft to counter vibration, and a low center of gravity for improved handling in corners.

While the auto maker has yet to issue any technical details of the turbodiesel, it is believed to displace 2.2L.

There is common-rail injection with four valves per cylinder in a DOHC layout, with combustion chambers recessed as symmetrical bowls in the piston crowns. The cylinder block and heads are light alloy castings, similar to Subaru's gasoline engines.

An injection timing chain handling both cylinder banks is combined with a multi-groove belt to drive the coolant, oil and steering pumps. A variable-geometry turbocharger and wastegate are integrated with the close-coupled particulate filter and primary exhaust system.

With the North American market critically important for Subaru, it sees the new engine as benefiting from the gradual acceptance of diesel powerplants.

However, the new mill primarily is aimed at Europe, where Subaru's sales reached a record 70,000 cars last year, with a target of 100,000 units set for 2009.

Meanwhile, Subaru is linking with Toyota Motor Corp. for the development of a hybrid-electric powertrain for its gasoline and diesel boxer engines.

However, Subaru's iconic all-wheel drive system does not easily adapt to Toyota's front-wheel-drive-based Hybrid Synergy Drive used in the Prius. To counter this, Subaru now is considering utilizing a version of the rear-wheel-drive hybrid powertrain used in the Lexus GS 450h sedan.