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Published byDebra Ward Modified about 1 year ago

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Applied Math Compression Ratio

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Compression

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Compression Ratio BDC TDC Compression ratio = BDC TDC

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10 cu in Compression Ratio TDC Compression ratio = BDC TDC 90 cu in Compression ratio = BDC TDC 90 cu in 10 cu in BDC Compression Ration = 9 to 1

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45 cu in + 7 cu in 45 cu in Compute 7 cu in Compression ratio = BDC TDC Swept Volume of Piston + Clearance Volume Clearance Volume Compression ratio = 7 cu in Compression ratio =7.4 to 1

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740 cu cm + 78 cu cm Compute Compression Ratio Intro Problem Determine the compression ratio: Swept Volume = 740 cu cm Clearance Volume = 78 cu cm Compression ratio = BDC Cylinder volume + Clearance Volume TDC Clearance Volume Compression ratio = 78 cu cm =10.5 to 1

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Changing the Piston Shape General assumption: Flat top pistons. How would the compression ratio change if dished pistons or pistons with valve relief cutouts were used instead? Valve Relief 8.6 cc

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740 cu cm cu cm Compute Compression Ratio Piston Shape: dished Determine the compression ratio: Swept Volume = 740 cu cm Clearance Volume = 78 cu cm Compression ratio = Cylinder volume + Clearance Volume Clearance Volume Compression ratio = 86.6 cu cm = 9.5 to cc valve relief cu cm It was 10.5 to 1 before the piston change

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Compute Compression Ratio Piston Shape: dished Conclusion: Pistons that are dished or have valve relief cutouts will lower compression ratio (if everything else stays the same).

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Changing the Piston Shape Dome How would the compression ratio change if domed pistons are used instead? Ford 351 Cleveland Dome =12 cc

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740 cu cm + 66 cu cm Compute Compression Ratio Piston Shape: Dome Determine the compression ratio: Swept Volume = 740 cu cm Clearance Volume = 78 cu cm Compression ratio = Cylinder volume + Clearance Volume Clearance Volume Compression ratio = 66 cu cm = 12.2 to cu cm It was 10.5 to 1 before the piston change 12 cc dome

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Compute Compression Ratio Piston Shape: Dome Conclusion: Pistons that are domed will raise the compression ratio (if everything else stays the same).

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Compute Compression Ratio Problem 2 Bore = 3.985” Stroke = 3.000” Clearance Volume = 4 cu in Compression ratio = Cylinder volume + Clearance Volume Clearance Volume cu in + Clearance Volume cu in + 4 cu in 4 cu in = to 1

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1 Compute Compression Ratio Problem 3 Bore = 4.000” Stroke = 2.870” Deck Height = 0.015” Head Gasket Thickness = 0.045” Combustion Chamber = 58 cu cm Compression ratio = Cylinder volume + Clearance Volume Clearance Volume cu cm cu cm cu cm 1 cu in cu in 1 x = = cu cm

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Clearance Volume Deck Height Compressed Gasket Thickness Volume of combustion chamber Bore = 4.000” Stroke = 2.870” Deck Height = 0.015” Head Gasket Thickness = 0.045” Combustion Chamber Volume = 58 cu cm

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cc’ing a cylinder head Burette Plexiglass Cylinder head Pictures from Auto Math Handbook by John Lawlor Published by HP Books

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Combustion Chamber Volume Deck Height Compressed Gasket Thickness 58 cubic centimeters

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Combustion Chamber Volume Deck Height Compressed Gasket Thickness 58 cu cm 0.015” 4.000” 0.045” 0.045” ” 0.060” Clearance Volume = 58 cu cm cu cm cu cm cu in x cu cm

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Bore = 4.000” Stroke = 2.870” Deck Height = 0.015” Head Gasket Thickness = 0.045” Combustion Chamber Volume = 58 cu cm Compute Compression Ratio cu cm 58 cu cm cu cm Compression ratio = Cylinder volume Clearance Volume cu cm cu cm = 9.40 to 1

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Dished Piston Or flat top piston with valve relief cut outs Affect on Overall Clearance Volume: Domed Piston Affect on Overall Clearance Volume: Other Things to Consider Piston Shape Adds to Overall Volume Takes away from the overall volume

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Practice Compression Ratio Worksheet

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