The philosophy of all-wheel drive “Subaru” states: all units, from engine pistons to the rear differential, must lie in the same plane. Hence, such advantages as a lowered center of gravity and almost imperceptible vibrations. One can argue whether this is really necessary, but the fact remains - all the engines of this company are opposed and have cylinders “lying on their sides” in the same plane with the crankshaft. And since European consumers increasingly prefer diesel, they had to start developing such an engine with an opposed layout - there’s simply nowhere to buy a finished one on the side.
In 2008, Legacy and Outback became the world's first mass-produced passenger cars with boxer diesel engines. It complies with Euro IV standards and is not only smooth in operation, but also atypical for a diesel engine with a fast response to the gas pedal - the inertia reduced due to the absence of balancing shafts affects. And what had to be changed in the gasoline engine, which served as the prototype of the novelty?
First of all, the cylinder block. The distance between the axes of the latter was reduced from 113 to 98.4 mm, as on gasoline “sixes, ” which did not hinder the placement of cooling channels between the cylinders. The piston stroke increased by 11 mm, and the cylinder diameter, in contrast, decreased by 6 mm. As a result, the entire block became 60 mm shorter compared to gasoline 2-liter engines.
The increased pressure in the combustion chamber forced not only to make the pistons out of a more durable material, but also to organize oil cooling specially for them. Of course, the gas distribution in the head has also changed dramatically, and in the camshaft drive the chain replaced the belt.