Subaru Updates Four-Cylinder Boxer Engines

[Human]

From Leftlanenews (This one's for you Martin )

Subaru today proudly announced the unveiling of its latest and third-generation four-cylinder Boxer engines, in both 2.0-liter and 2.5-liter displacements.
This latest generation marks the first major refresh of the engines in 21 years, marking both a tribute to the forward thinking of the original design, and the need to update the engine as emissions and power requirements continue to develop new standards.
Subaru says that the third-generation Boxer engine has been rejuvenated from the ground up, retaining only the basic design of the horizontally-opposed layout. The changes have resulted in an approximate increase in fuel economy of 10 percent, as well as increased smoothness and an improved power band. More specifically, the bore and stroke have been modified to allow for a more compact combustion chamber, as well as a longer stroke.
These two changes were previously impossible due to the chassis mounting locations. Other changes include the optimization of intake and exhaust valves, with the intake side receiving an intermediate lock system which allows valve timing to be advanced or delayed for more precise control over intake and exhaust valve timing - all of which contributes to improved overall engine performance from both power and emissions output perspectives.
The latest Boxer engines also received improved cooling by adding a separate engine cooling circuitry for the block and head, as well as the use of lightweight pistons and rods, along with a highly efficient oil pump that creates a 30 percent reduction in friction loss.
The 2.5-liter variation retains the same 170 horsepower rating, albeit with peak power at a slightly lower rpm, while torque improves from 170 lb-ft at 4,400 rpm to 174 lb-ft at 4,100 rpm.
The engine was also designed in a way that is as forward thinking as the original design, with the intention of allowing future changes to be implemented without a major redesign as environmental standards continue to evolve.

 

[martinbo]

From FHI's press release:

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 environmental measures.

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 popular name.

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 2,000 cc displacement, both with 4 cylinders. These models will now be positioned as our main engines.

・ 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.

 

[Monster]

No direct fuel injection?

 

[martinbo]

New Boxer engine ~~~ Current engine
Engine type: Horizontally-Opposed 4 cylinder DOHC ~~~ Horizontally-Opposed 4 cylinder DOHC
Displacement: 1,995 cc ~~~ 1,994 cc
Compression ratio: 10.5 ~~~ 10.2
Bore x Stroke: 84 x 90 mm ~~~ 92 x 75 mm

So, some interesting developments/disappointments here:

1. The move to an Audi-esque undersquare engine architecture from an oversquare one is a surprise. The narrow bore / long stroke layout does have benefits however and Audi themselves have proven that long-strong engines can be made to rev as quickly as their shorter stroke counterparts. Of course, by going with a narrower bore, Subaru effectively shortens the Boxer engine which will have benefits in the area of weight distribution ahead of the front axle. How this layout will affect future turbocharged WRX and STI-type engines remains to be seen.

2. Lack of Direct Injection is a disappointment; FHI does suggest that the engine is designed with scalability and adaptability in mind so perhaps DI is on the cards in 2097.

3. Typically FHI, there's a general lack of information about the new engine such as weight, valvetrain drive mechanism (still belt-driven or a move to chain?), internal engine designations etc...

As for the engine outputs as quoted by Leftlane some posts above, I don't know where they got the numbers for the 2.5 litre engine as I can only find official information for the 2.0 litre JDM engine.