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Engine Calculations

Engine Calculations. Displacement, Compression Ratio, Horsepower, Torque. Displacement. The volume of the cylinder between the top dead center and bottom dead center positions of the piston Does not include the combustion chamber or other non swept space in the cylinder.

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Engine Calculations

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  1. Engine Calculations Displacement, Compression Ratio, Horsepower, Torque

  2. Displacement • The volume of the cylinder between the top dead center and bottom dead center positions of the piston • Does not include the combustion chamber or other non swept space in the cylinder

  3. Displacement Formula • Cylinder displacement • CID = ( )2 x 3.14 x Stroke • Engine displacement • Cylinder Displacement x Number of Cylinders • Displacement conversions • In3 x 16.4 = cm3 (cc’s) • Cm3 divided by 1000 = Liters Bore 2

  4. Example • Bore = 4.030” • Stroke = 3.48” • 8 cylinder engine • CID = ( )2 x 3.14 x 3.48 • CID = (2.015)2 x 3.14 x 3.48 • CID = 4.060 x 3.14 x 3.48 • CID = 44.367 in3 • 44.367 in3 x 8 cylinders =354.9 in3 4.030 2

  5. Example Cont’ • 354.9 in3 x 16.4 = 5820 cm3 • 5820 cm3 divided by 1000 = 5.8 Liters

  6. Compression Ratio • The ratio between the volume of the cylinder at BDC and the volume of the cylinder at TDC

  7. Compression Ratio Formula • Compression ratio = V1 + V2 +V3 +V4 V2 +V3 +V4 • V1= Cylinder displacement volume • V2 = Deck clearance volume • V3 = Head gasket volume • V4 = Combustion chamber volume

  8. Example • .010 Deck clearance • .041 Compressed head gasket thickness • 64 cc combustion chamber (64cc / 16.4 = 3.90 in3) • 44.367 in3 + .127 in3 + .523 in3 + 3.90 in3 .127 in3 + .523 in3 + 3.90 in3 • 10.75:1 Compression ratio

  9. Engine Factors Affecting Compression Ratio • Piston design • Head design (flat top, dish, dome, valve reliefs) • Compression height – distance from the centerline of the piston pin to the top of the piston • Ring height • Deck height – distance from the centerline of the main journals to the block deck surface • Bore • Stroke • Combustion chamber size • Valve head design (flat, dished, domed) • Head gasket thickness (and design)

  10. Torque • Twisting force • Measured in lb/ft

  11. Horsepower • Calculated from torque and RPM measurements • One horsepower is the power needed to lift 550 pounds one foot in one second • Horsepower = Torque x RPM 5252 • Horsepower and torque values are always the same at 5252 RPM’s

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