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Fuji Heavy Introduces Third-Generation Subaru Boxer Engine; Approximately 10% Improvement in Fuel Efficiency

Third-generation Subaru Boxer engine. Click to enlarge.

Fuji Heavy Industries Ltd. (FHI) has developed a third-generation boxer (horizontally opposed) engine—the first overall renewal for the platform in 21 years. A Boxer engine was first employed in the Subaru 1000 in 1966. The second-generation boxer engine was introduced in the first Legacy models in 1989.

Third generation improvements include an approximately 10% improvement in fuel efficiency, and improved driving performance for smooth acceleration in all speed ranges. Furthermore, FHI designed the new engine with consideration of the technology’s expandability and potential capability to receive further upgrades meeting future environmental measures.

This new-generation 4-cylinder gasoline engine was entirely renewed, starting from the basic structure to allow a longer stroke than current engines. The new engine is available with 2,500 cc or 2,000 cc displacement, both with 4 cylinders. Features of the third generation include:

  • The bore and stroke, the basic structure of this engine, have been reviewed to achieve a compact combustion chamber as well as a long stroke, which was difficult previously due to chassis mounting conditions in boxer gasoline engines. This allows high combustion efficiency, and generates a sufficient mid-low speed torque with improved fuel efficiency and practicality.

  • Improved fuel efficiency has been achieved through optimization of intake port configuration and the addition of partitions inside ports, the use of TGV (Tumble Generated Valve), and the use of an EGR (Exhaust Gas Recirculation) cooler.

  • AVCS (Active Valve Control System) is used on both intake and exhaust valves. For the intake side in particular, an intermediate lock system allows valve timing to be advanced or delayed for precise control over intake and exhaust valve timing, allowing maximum engine performance in output, fuel efficiency, and exhaust emission.

  • The use of lightweight primary moving parts, such as pistons and connecting rods, and a highly efficient and compact oil pump provides an approximately 30% reduction in friction loss and improves fuel efficiency and revolution response.

  • Cooling has been optimized by using separate engine cooling circuitry for the block and the head, resulting in improvements in fuel efficiency and output characteristics.

Subaru Boxer Engines
 3rd generation Boxer2nd generation Boxer
Engine type Horizontally-Opposed
4-Cylinder DOHC
4-Cylinder DOHC
Displacement 1,995 cc 1,994 cc
Comp. ratio 10.5 10.2
Bore x Stroke 84 x 90 mm 92 x 75 mm
Max. output 109 kW 109 kW
Max torque 196 N·m 191 N·m

All the advantages of the horizontally-opposed layout were maintained: lightweight, compact, low center of gravity, and superior vibration balance.

FHI has built a new factory at the Gunma Oizumi Plant exclusively for the production of this new-generation boxer engine.



Stroke this, port that, What a load of BS.

ICE manufactures ONLY ever quote fuel efficiency, NEVER energy efficiency. They are not the same.

This thing still has pistons going up and down and camshafts pushing spring loaded valves, it still runs at 25% energy efficiency as every other petrol ICE before it. A triple expansion steam engine is more energy efficient.

EVs are the future guys, get with the program!


Paul is generous at 25% efficiency. The average is closer to 18%.


Not up and down. Side to side.


EVs will be the future when lower cost batteries with higher energy and power densities become available.

Until then EVs will be a rich man's toy or pie in the sky.


A 10% improvement over 20 years is about 2% a year. EV batteries will do much better than that.


I checked the EPA raings for this engine in a Forester with manual transmission-
guess what? no meaningful improvement 2011 vs 2010.
Where's the 10 % improvement???

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