Subaru's Third-Generation Boxer Engine – Click above for high-res image
Subaru first deployed its horizontally opposed Boxer engine back in 1966. Twenty-three years later, the second-generation Boxer debuted in the 1989 Legacy. Now, after 21 years of success, Fuji Heavy Industries Ltd. (FHI), parent company of Subaru, is ready to reveal the third-generation Boxer engine.
Third-generation improvements are aimed at improving fuel efficiency and driving performance. This all-new Boxer mill features a lengthened stroke, a compact combustion chamber, optimized intake ports and employs an EGR (exhaust gas recirculation) cooler. Additional modifications include the use of lightweight internals, an AVCS (active valve control system), improvements to the cooling system and a compact oil pump.
The third-generation Boxer engine maintains all of the benefits of the horizontally-opposed layout: compact, low center of gravity and lack of vibration, but the mill now boasts a claimed 10-percent improvement in efficiency and the ability to meet looming emissions standards. FHI will build the latest Boxer engine at its newly-constructed factory within the confines of its Gunma Oizumi Plant.
[Source: Fuji Heavy Industries]
FHI Develops a New-generation Subaru Boxer Engine
-- New Horizontally-Opposed engine, providing superior combination of environmental friendliness
and enjoyable driving --
Tokyo, September 23, 2010 - Fuji Heavy Industries Ltd. (FHI) has developed its new-generation boxer engine*
that combines the technology and know-how used in Horizontally-Opposed Boxer engines, the core technology
that has supported Subaru's unique driving since it was first employed in the Subaru 1000 in 1966. This overall
renewal is the first in 21 years, since the second generation boxer engine was introduced in the first Legacy
models in 1989.
This new-generation Horizontally-Opposed 4 cylinder gasoline engine, the third generation Subaru boxer engine,
showcases Subaru's latest engineering research and development. It offers a new performance level by further
refining Subaru's unique expertise in Boxer engine technology. The engine was entirely renewed, starting from the
basic structure, while all the advantages of the horizontally-opposed layout were maintained: lightweight, compact,
low center of gravity, and superior vibration balance. New-generation improvements include advances in both
environmental friendliness, such as an approximately 10% improvement in fuel efficiency, and 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
FHI built a new factory at the Gunma Oizumi Plant exclusively for the production of this new-generation boxer
engine. This new plant offers state-of-the-art production facilities that make full use of FHI's engine
manufacturing know-how developed to date, as well as a highly efficient production system delivering products
meeting the highest quality standards.
* Boxer engine: Also known as a Horizontally-Opposed engine. In this design, the pistons are arranged symmetrically left
and right along the crankshaft. When the pistons move, they resemble the punches thrown by boxers, thus resulting in this
[Major Features of the New-generation Subaru Boxer engine]
The overall structure of this engine has been totally renewed, by reviewing the bore and stroke for the basic structure to
allow a longer stroke than current engines. It is designed to achieve high efficiency in basic performance, allowing the
smooth and sporty rotational properties for which Horizontally-Opposed engines are known, while also making
improvements in practical torque and environmental friendliness. This engine is available with 2,500 cc or 2,000cc
displacement, both with 4 cylinders. These models will now be positioned as our main engines.
The New-generation Subaru Boxer engine
・ 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
・ 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
・ 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
・ 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.
FHI is fully committed to develop new products on the theme of integrating enjoyable and reliable driving with
environmentally friendly solutions. This same theme applies to this new-generation boxer engine, which will be
positioned as a main engine and the starting point of its future power unit strategy. Starting with the Forester, the
new engine will be deployed in other Subaru products in the future.
About Fuji Heavy Industries Ltd.
Fuji Heavy Industries Ltd. (FHI), the maker of Subaru automobiles, is a leading manufacturer in Japan
with a long history of technological innovations that dates back to its origin as an aircraft company. While
the automotive business is a main business pillar, FHI's Aerospace, Industrial Products and Eco
Technologies divisions offer a diverse range of products from general-purpose engines, power generators,
and sanitation trucks to small airplanes, crucial components for passenger aircrafts, and wind-powered
electricity generating systems. Recognized internationally for its AWD (all-wheel drive) technology and
Horizontally-Opposed engines in Subaru, FHI is also spearheading the development of environmentally
friendly products and is committed to contributing to global environmental preservation.