The innovators: the first horizontally opposed diesel engine
The cars we drive today were influenced by these pioneers First horizontally opposed diesel engine Subaru Forester/legacy 2008
Automotive innovators aren’t always what you’d expect. Sometimes less commercially successful technological ventures can be just as fascinating from an automotive standpoint.
A prime example is Subaru’s EE boxer diesel engine; a valiant but ultimately flawed take on a much-loved staple of internalcombustion technology.
In the mid-2000s – before #dieselgate and the groundswell surrounding EVS was little more than a tremor on the mobility Richter scale – diesel engines were the powerplant of choice in Europe.
With a lineup largely made up of flat-cylinder petrol units, Subaru felt it prudent to introduce a diesel engine to its growing SUV stable to remain competitive. However, instead of going with the safe option of an inline-cylinder unit from parent company Toyota, in 2005, the firm decided to stick to its boxer-engine roots and develop the first commercially available boxer diesel.
Heritage aside, Subaru saw numerous advantages in opting for a flat-cylinder arrangement for its EE20 engine. With its horizontally opposed cylinder layout, the unit was more resistant to the vertical and lateral mechanical forces within the cylinders and crankshaft during the four-stroke combustion process. This balanced setup also allowed Subaru to do away with the complex, and weight penaltyincurring, balancer shaft.
Although the horizontal layout meant the engine’s packaging took up more space width-wise in the engine bay, it allowed Subaru’s engineers to mount the unit further down in the car, lowering its centre of gravity. Factor in greater thermal efficiency and a mechanically more direct route for power transfer between the engine and transmission, among other virtues, and the concept of a boxer diesel looked like the blueprint for the ideal engine.
The common-rail 2,0-litre made its debut in the 2008 Forester, where it made 110 kw and 350 N.m while trimming between 15% and 20% off the fuel consumption figures of the equivalent 2,0-litre EJ petrol model. Our experiences with Subaru’s boxer diesels were certainly positive; the Outback 2,0 Diesel Lineartronic we tested a few years ago gained plaudits for its uncharacteristically smooth manners and frugality.
Although this combination of positive traits may have looked great on paper, the bursting of the diesel bubble in 2015 would play a major part in the EE20’S demise. Ever-more stringent standards in the wake of the diesel emissions scandal made it difficult for Subaru’s engineers to realistically meet mandated CO2 targets.
The company’s focus turned towards downsized turbopetrols and the innovative EE20 was discontinued in 2020. The timing of its arrival and caprices of emissions legislation may have robbed the EE20 of the success it rightly deserved but its standing as the only commercially available boxer diesel still means it’s an innovator in its own right. And, as such, we salute it for that.