Key facts
- Subaru is targeting 50% thermal efficiency for its next-generation boxer engine, according to the company.
- The development prototype is a direct-injection turbocharged engine; the reference powertrain is naturally aspirated.
- Subaru said the development engine has roughly twice the high-efficiency operating range of its current hybrid engine.
- Subaru is evaluating a variable-geometry turbocharger, the Miller cycle and pre-chamber combustion to help reach the target.
- Subaru has no plans to abandon the boxer engine and aims for a design usable in both gasoline vehicles and hybrids.
Subaru is working to improve the fuel economy of its mainstay boxer engine, aiming for a standard design able to power both gasoline vehicles and the hybrids it wants to sell in the US, the company said on November 15, 2026.
The Japanese automaker has no plans to abandon its signature horizontally opposed layout. At a development strategy briefing at the Subaru Research and Experiment Centre in Sano, Tochigi Prefecture, Subaru said its next-generation boxer is targeting 50% thermal efficiency, a measure of how much of the energy in fuel is converted into useful work.
According to data Subaru presented, the development engine has roughly twice the operating range with high thermal efficiency compared with the naturally aspirated engine currently used in its hybrid models. The prototype is a direct-injection turbocharged engine, whereas the reference powertrain is naturally aspirated.
Subaru is evaluating several technologies that could help push thermal efficiency closer to the 50% target, including a variable-geometry turbocharger, the Miller cycle and pre-chamber combustion. The company acknowledges that these technologies alone probably will not be enough to reach the target, and it remains open when a new boxer generation could enter series production.