How to Calculate the Displacement of a Cylinder

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Old-timers will tell you that there's no replacement for displacement; after all, an engine is only capable of creating as much power as the air and fuel in its cylinders can produce. More displacement means more air and fuel, which means more power. While old-school wisdom falls apart in light of power additions like nitrous, turbos and supercharging, cylinder displacement remains one of the most important and basic of all engine specifications.

  • Calculate displacement from cylinder bore and piston stroke. Divide the cylinder bore in inches by two to obtain the cylinder radius. Multiply that figure by itself, and then multiply that by 3.141 (pi). Multiply this figure by the stroke for the displacement of a single cylinder. Multiply by the number of cylinders for the displacement of the engine.

  • Figure cylinder displacement from engine displacement in cubic inches or liters. Divide the engine's displacement by the cylinder count for the displacement of each cylinder. Ensure that you're going by the engine's actual displacement, and not the factory advertised displacement. As in the Pontiac example later in this article, manufacturers often round displacements off to the nearest tens place for advertising purposes.

  • Convert to or from metric. For metric measurements, multiply the engine or cylinder's actual displacement in cubic centimeters by 0.061 to convert it to cubic inches. If you have the displacement in cubic inches and want to convert to cubic centimeters, multiply the cubic inches by 16.38. If you have the displacement in cubic inches and want to convert it to liters, multiply the cubic inches by 0.01638.

Tips & Warnings

  • Use this example for calculations. A Pontiac 350 V-8 has a bore of 3.88 inches and a stroke of 3.75 inches. Divide the bore (3.88) by two to get the radius (1.94). Multiply that by itself (1.94 x 1.94 = 3.76), multiply by pi (3.76 x 3.141 = 11.82), then multiply that by the stroke to yield the displacement of one cylinder (11.82 x 3.75 = 44.33 cubic inches). Multiplying that by eight, (the cylinder count), the 350's actual displacement comes out to 354.62 cubic inches. To get cubic centimeters, take 354.62 cubic inches multiplied by 16.38 equals 5,808 cubic centimeters. To get the engine's liters, take 354.62 cubic inches and multiply by 0.01638 to arrive at 5.8 liters

References

  • "Auto Fundamentals"; Martin T. Stockel, Chris Johanson; 2000
  • "Race Car Engineering & Mechanics"; Paul Van Valkenburgh; 2004
  • Photo Credit Jupiterimages/Comstock/Getty Images
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