![]() This equates to 0.13 cubic inches, or 2.1 cc. Our piston is 0.010-inch below the deck at top dead center. Volume = (Cylinder Diameter / 2) Squared x height This affects the clearance volume of the engine and must be calculated. The block deck height, piston compression height, rod length, and stroke all affect how much a piston is "down" or "out of the hole" when at top dead center. (If you don't know, you can use a cc'ing kit to measure it.) Remember: dish volume increases clearance volume, and dome volume reduces clearance volume. Most piston manufacturers list the volume of the dish or dome of their pistons. This includes the piston dish/dome, deck, head gasket, and combustion chamber volume.Ĭlearance Volume = Piston Volume + Deck Volume + Gasket Volume + Combustion Chamber Volume Important: we need to keep our units consistent, so it's easiest to convert this volume into cubic centimeters (cc).ġ cubic inch = 16.387 cubic centimeter (cc) Swept Volume = (Cylinder Diameter / 2) Squared x 3.14 x Strokeįor an engine with 4.030-inch bore and a 3.00-inch stroke, the result is 38.2 cubic inches (one cylinder of a 306 cubic inch engine). Head Gasket Compressed Thickness = 0.039-inchįirst, let's figure the swept volume of one cylinder:.The formula for the Engine Compression Ratio is:Ĭompression Ratio = (Swept Volume + Clearance Volume) / Clearance Volume The total volume includes the swept volume (bore x stroke) and the clearance volume (piston dish/dome, deck, head gasket, and chamber volume). Combustion chamber design is also a large factor in compression ratio. Measure this with a dial indicator and magnetic base. Whether the piston is above deck or in the hole at top dead center also affects compression ratio. Most piston manufacturers list the volume of their pistons. Piston design has a large impact on compression ratio. The ratio of the two different volumes is the compression ratio. Measure the water it took to fill the cylinder with the piston at bottom dead center, and then divide that by the amount of water needed to fill the cylinder with the piston at top dead center. Imagine if you unscrewed one of the spark plugs and filled the cylinder with water. Compression Ratio is the total volume of the engine divided by the clearance volume of the engine. Compression ratio determines the type of fuel, how much boost, and has a significant influence on an engine's power and torque potential. The compression ratio isn't just a number: it's one of the greatest determining factors in engine building. INSTRUCTIONS: Choose units and enter the following Įngine Compression Ratio (CR): The ratio is returned as a real number. The Engine Compression Ratio calculator computes the compression ratio based on the cylinder bore (diameter), stroke length and the clearance volume.
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