The internal combustion engine isn't going down without a fight. Toyota, Mazda, and Subaru made that abundantly clear when they announced a joint effort to develop new combustion engines in 2024. Rather than sharing the same powertrain, each automaker would pursue its own technology: Toyota would work on a new family of smaller, more efficient four-cylinder engines, Mazda would continue developing its rotary and a new inline-four Skyactiv-Z, and Subaru would stick with its beloved horizontally opposed boxer.

Since then, Toyota and Mazda have offered more details about their respective plans. Subaru, however, has been relatively quiet about what comes next for its signature engine layout. That's finally changing, with the Japanese automaker providing a closer look at its next-generation boxer and revealing an ambitious target: 50 percent thermal efficiency.

The goal isn't simply to keep the flat-four alive for nostalgia's sake. Subaru wants to make it significantly more efficient without sacrificing the driving characteristics that have defined its cars for decades. Engineers are looking for ways to improve combustion without fundamentally changing the layout. They've been working on creating stronger airflow inside the cylinders, helping air and fuel mix more thoroughly before ignition.

Japanese magazine Motor-Fan attended a Subaru briefing about its next-generation engine, where the company revealed promising early results. Despite retaining a relatively short stroke, the development boxer already generates stronger airflow inside the cylinders than competing benchmark engines. Subaru has also introduced three-dimensional combustion analysis to its development process. This allows engineers to predict better how flames spread inside the cylinders after ignition, making it easier to anticipate knocking and optimize combustion.

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