Subaru Boxer vs. Atkinson cycle engine ? Reliability and Longevity?


Asked by Jul 25, 2015 at 11:50 PM about the 2010 Subaru Outback 2.5i Limited

Question type: General

Could you please explain why the Atkinson cycle Inline Four is more popular than the flat
Four horizontally opposed Boxer engine?   Is it because of production costs or some
other reason.   Other than Porsche,  Subaru is the only other major car manufacturer to
stand by this design.  A real niche market.   Do you really think it costs more to maintain?

6 Answers


Here's some info on this, big-difference-between-a-boxer-and-flat-engine-85305.html

3 out of 3 people think this is helpful.

And , some more information, please comment,

David Morris

Boxer engine is used for both the Scion FR-S and Subaru BR-Z. Toyota would've never agreed to use it in the FR-S if there were reliability or high cost concerns. But both cars are new, so we'll see how they hold up...Although they aren't selling too well, both are awesome cars!


James, while these are new models, the boxer engine is by no means a new engine. And, Toyota has a share in Subaru. Both the FRS and the BRZ share some similar components. Do you have any comments on the efficiency of the flat engine design over the traditional inline Four. The design of the engine means there's no counterweight balance on the crankshaft. Also, rather than pushing up and down against gravity, these engines move side to side. What do you think?

1 out of 1 people think this is helpful.
Michael Eby

Not all inline fours use the Atkinson cycle, which is often used on hybrids and keeps the intake valve open longer to increase efficiency at the cost of horsepower. (In other words, Subaru could adapt the Atkinson cycle to the flat-four as well). Subaru's flat-four engines are easily as fuel-efficient as an equivalent inline design, and (although arguably a bit noisy) have notably less vibration than an inline engine as the second-order vibrations cancel out. They are low, lightweight and fit well with Subaru's AWD system. The biggest disadvantages of the flat-four are the wide design (which would not work well mounted transversely) and the added complexity of two sets of camshafts/valves/heads instead of one.


Yes, appears that you're conflating apples and oranges again. Maybe that's why responses are withheld?

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