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Converting the ignition of a fuel-air mixture into usable mechanical energy lies at the core of a dizzying number of internal combustion engines developed over the course of more than century. Although typical piston engines with a cylinder head and valve-train are the most common by far, and even rotary engines are quite well-known, the opposed-piston engine design is significantly more obscure. In a recent video by [driving 4 answers] , this type of engine is covered and why it’s actually a pretty nifty ICE design with many benefits.

Achates opposed-piston design. (Source: driving 4 answers, YouTube)

" data-large-file="https://hackaday.com/wp-content/uploads/2026/05/opposed_piston_engine_achates_driving_4_answers_youtube.jpg?w=625" src="https://hackaday.com/wp-content/uploads/2026/05/opposed_piston_engine_achates_driving_4_answers_youtube.jpg?w=400" alt="Achates opposed-piston design.…