The Opposed cylinder design for gasoline engines is rather uncommon, though several have been made in the past.

The expansion forces in an opposed cylinder engine are balanced. For ever force there must be an equal and opposite force. Thus V shaped cylindar arrangements create forces that cause the engine block to vibrate. This seems like waste of energy.

Napier Deltic engines, a type of opposed cylindar engine, are described as "high strung" and require more maintenance. I would expect the same of any opposed cylinder design due to the use of gears instead of a single crankshaft. Ignoring the maintainence issue, is the opposed cylindar design more efficient at burning fuel?

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    $\begingroup$ The boxer engine will also reduce vibration and is more traditional in piston chamber access. $\endgroup$ Feb 5, 2016 at 17:06
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    $\begingroup$ A R6-engine is fully balanced and does not vibrate. A V12 either. Therefore, they are such good engines and BMW used them for such along time. Disadvantage of Bx, R6 and V12 is, that they consume a lot of space where no space is available (B) or in general (V12) or consume no space, where it is available (R6). $\endgroup$ May 22, 2016 at 11:41

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These opposed cylinder engines have the same working of a 2-stroke engine . 4 Stroke engine is more efficient primarily because of the presence of valves which precisely control the flow of charge into the chamber and exit the exhaust gases with proper timing which is hard to achieve by ports in a 2 stroke engine. The mileage of 4 stroke is greater and moreover running a turbocharger with extra crankshaft and gearing mechanisms will require a high power diesel engine that reduces the effectiveness of turbocharger due to low speeds hence it further decrease efficiency . Due to two piston compression there is high compression ratio and produces lot of heat and there is very less space for implementing an effective cooling system this will reduce the thermal efficiency. Hence even though it can produce more power than a 4 stroke it has a lot of efficiency losses.

  • $\begingroup$ Have you heard of any four cylindar opposed cylindar engines? $\endgroup$
    – Dale
    Jun 18, 2016 at 0:10
  • $\begingroup$ Fairbanks-Morse made OP diesel engines for subs and other applications. These engines ran a 2-stroke diesel cycle and could be had in configurations of 4-12 cylinders. Most main engines were either 9 or 10 cylinder models, and some engines were used to drive emergency generators on surface vessels, either naval or civilian. $\endgroup$
    – user16622
    Jun 18, 2016 at 15:42

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