The Boxer Engine Still Has a Future
Subaru’s commitment to its boxer engine has become a little harder to read. A recent announcement about the powertrain’s future in Europe raised questions about whether the Japanese automaker was slowly moving away from its signature engine. Its work on a dedicated EV platform has added to the speculation, particularly with a mysterious electric prototype raising hopes for a possible STI comeback.
But there’s another side to the story. Reports from a development strategy briefing in Japan suggest Subaru isn’t ready to abandon internal combustion. The automaker is developing a next-generation horizontally opposed gasoline engine, with a rather ambitious 50% thermal efficiency target.
Subaru Is Rethinking How Its Boxer Engine Works
Getting there won’t be straightforward. The boxer engine’s wide layout limits piston stroke, making it harder to adopt one of the conventional approaches to improving thermal efficiency.
Subaru is instead focusing on combustion. Its development engine uses straighter, narrower intake ports to increase airflow velocity and create a more uniform air-fuel mixture. Supercharging compensates for the pressure losses caused by the smaller passages.
The company is also using 3D combustion analysis to better predict knocking and control flame propagation. According to Motor Fan, the development engine has roughly twice the high-efficiency operating range of its conventional engine benchmark.
Other technologies being explored include variable geometry turbocharging, the Miller cycle, and pre-chamber combustion. The latter uses a smaller chamber to ignite the mixture before sending jets of burning gases into the main combustion chamber, potentially making leaner combustion possible.
Subaru admits that reaching 50% thermal efficiency remains difficult. However, it’s important to note that these are still development technologies, not confirmed production specifications.
Keeping Its Options Open Makes Sense
Subaru’s strategy resembles Toyota’s approach to powertrains. Neither company appears interested in putting all its eggs in one basket. And that makes sense. The automotive industry is changing quickly, but not every market is moving toward electrification at the same pace. Gasoline engines, hybrids, and EVs will likely coexist for years.
For Subaru, improving the boxer engine keeps an important part of its identity relevant while its electric vehicle plans take shape. An electric STI could eventually happen. But that doesn’t mean the boxer has to disappear. In an industry this unpredictable, having more than one path forward might be Subaru’s smartest move.
Subaru
