2023 Subaru Impreza

Boxer

2.5L Naturally Aspirated Flat-4

The horizontally-opposed pistons punch outward like a boxer's fists, giving a low, flat center of gravity and that unmistakable off-beat thrum at idle. Power builds smoothly and linearly without turbo drama, prioritizing balance and surefooted predictability over outright punch.

Subaru has built only boxer engines for its cars since the 1966 EA series, and the FB25 is the third-generation gasoline flat-four, announced in 2010 to succeed the long-serving EJ. It is built at a dedicated facility in Oizumi, Gunma Prefecture, Japan.

• The FB program targeted roughly 10% better efficiency than the old EJ, partly via a claimed 28% reduction in internal friction.
• A 2019 'FB25D' revision added direct injection, refreshing the engine more than two decades after the layout's basic concept was set.
• Subaru is one of only two automakers (alongside Porsche) to keep building flat-engine passenger cars in volume.