Subaru Reinvents The Boxer Engine, Minus The Direct Injection

Paul Niedermeyer
by Paul Niedermeyer

There it is, Subaru’s all-new gen 3 engine, its first new boxer since 1989, and only the third since 1966 (full history here). As is obvious at first glance, Subaru has reverted to a DOHC head, after switching to a SOHC back in 2000. What’s not so apparent is that the internal architecture is very different: the boxer loses its oversquare (large bore/short stroke) configuration for… the opposite. Long strokes are in (again), favored for their compact combustion chambers and ideal torque curves. The new engine has a host of other goodies, and is expected to be 10% more efficient. But direct injection is not on the list. Nor is piston slap, hopefully.From Subaru’s Press release:

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 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.

The 2011 Forester will be the first recipient of the new motor, which will then spread across the line. Subaru has also announced its intentions for a hybrid version.

Paul Niedermeyer
Paul Niedermeyer

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  • MikeInCanada MikeInCanada on Sep 24, 2010

    Any news on a diesel making it to North America? There's Euro diesel version but I have no idea just how series of an effort it is on the part of Subaru.

  • Wmba Wmba on Oct 23, 2010

    I see some rather unsubstantiated claims about long stroke engines having better thermodynamic efficiency than short stroke ones. Can anyone cite some proper engineering references as to why this should be so? Because I've never run into any myself. In fact, the opposite claims are usually made. A larger bore allows bigger valves and better breathing, and the total distance for a flame front to travel from a central plug to the extremity of the cylinder is less, because the capacity of the cylinder increases as the square of the bore and only linearly with the stroke. Then. everyone goes on about long stroke engines having better torque. Hmm, like Hondas, you mean, which have a hard time removing the skins from rice puddings at low revs in my experience. Remember that a bigger piston puts more force onto the longer stroke, and there isn't much overall difference, as witness the old and new engines here. The only reason I can think of for the change is to make the pistons much lighter, and to make it easier to have a compact combustion chamber. But each ring will have to move farther and faster in the bore, and each rod big end will encounter more sliding friction on the crank. I'd have to say it's a bit of a wash, but allows the new engine to be more like the diesel casting. I'm open to anyone's referenced arguments as to the merits of a long stroke. But lowered volumetric efficiency with the smaller valves does not equate to higher efficiency, and the thermodynamic efficiency argument I've only read as anecdotes rather than real engineering findings.

  • MaintenanceCosts It's not a Benz or a Jag / it's a 5-0 with a rag /And I don't wanna brag / but I could never be stag
  • 3-On-The-Tree Son has a 2016 Mustang GT 5.0 and I have a 2009 C6 Corvette LS3 6spd. And on paper they are pretty close.
  • 3-On-The-Tree Same as the Land Cruiser, emissions. I have a 1985 FJ60 Land Cruiser and it’s a beast off-roading.
  • CanadaCraig I would like for this anniversary special to be a bare-bones Plain-Jane model offered in Dynasty Green and Vintage Burgundy.
  • ToolGuy Ford is good at drifting all right... 😉
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