They have been corrected to certain degree, but there is only as much as engineers can do without making the engine prohibitively heavy and expensive.Īdditionally, a boxer engine of equivalent displacement / performance is inherently heavier and more expensive than an in-line four. The issues that have traditionally plagued Subaru boxer engines (head gasket failures, oil consumption) are direct consequence of the boxer configuration. This issue with a boxer engine can be addressed to certain extent with careful engineering, but things like exterior temperature variations make it nearly impossible to match the level of thermal expansion control that can be achieved with a more compact, geometrically simple block of 4 in-line cylinders. Engineers can address this by either "beefing up" the engine making it heavier (and more expensive), or have to relax tolerances to prevent seizing under high stress. Under high torque, the block / cylinders deform more than in an in-line 4 of equivalent displacement / performance. A boxer configuration make is inherently more "flexible", which in is bad to keep tight tolerances. The result is that in-line engines can operate within tighter tolerances.Ģ) An in-line block is much more rigid (for same material usage / weight). Because the cylinder block is more compact in an in-line 4, it's easier to design a cooling system them will keep the entire block's temperature more uniform. In a boxer it is nearly impossible to keep uniform temperatures across the cylinder / head area. This makes the design much more complicated in terms of keeping tight tolerances in light of differential thermal expansion. Unlike an in-line four, where the "hot" area (upper cylinder & head) is compact and nicely grouped, in a boxer you have two "hot" extremes separated by a "cool" block. Here are the main two reasons why.ġ) A boxer has larger surface area-to-volume ratio. Actually, all other things being equal (materials, manufacturing tolerances, etc.), a boxer engine is, by design, more problematic than an in-line 4.
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