Compression ratio data for a 351 cubic inch motor



Compression ratio data for the Ford 351 Cleveland

(Vs) The swept area volume: 4” bore x 3.5” stroke = 43.98 cubic inches

1 cubic centimeter = 0.061 cubic inches

43.98 / 0.061 = 721 cc

(Vc) The clearance volume, is the volume above the top piston ring at

TDC, it is more than just the volume of the pocket in the cylinder head;

it is the sum of several small volumes. This includes the volume of the

pocket in the cylinder head plus the volume of the head gasket bore

plus the volume of the clearance between the top of the piston at TDC

and the cylinder block deck plus the volume of the valve notches in the

piston’s dome plus the volume of any dish in the piston’s dome plus

the volume of the clearance between the piston and cylinder wall above

the top ring. In the case of the oem 351C, the additional small volumes

add up to about nominal 17cc with flat top pistons having 2 valve reliefs.

(CR) compression ratio = (Vs + Vc) / Vc

The table below is computed for a standard displacement cylinder

having a swept area of 721cc. Vc is in units of cubic centimeters.

Vc…..CR

|Cleveland cylinder head combustion chamber volume |

|All volumes are nominal +/- 1.5 cc |

| |

|Australian 302C closed chamber heads: 57.9 cc |

| |

|’70 Boss 302 closed chamber heads: 58.5 cc |

| |

|’69 Boss 302 & ’70 4V closed chamber heads: 62.8 cc |

| |

|’71 Boss 351 & ’71 4V closed chamber heads: 66.1 cc |

| |

|Australian 351C open chamber heads: 73.7 cc |

| |

|’72 351 HO & ’72 CJ open chamber heads: 75.4 cc |

| |

|’73 – ’74 4V open chamber heads: 78.4 cc |

| |

|2V open chamber heads: 78.4 cc |

| |

|’73 – ’74 Q code dished pistons: add 8 cc |

| |

|Zero decked block: subtract 5 cc to 7 cc (1 cc per 0.005”) |

| |

|The piston of the '72 351 HO had a 0.007" greater compression height: subtract 1.5cc |

| |

|To use this info, add 17cc plus the combustion chamber volume to determine your Vc then |

|reference the chart to find the compression ratio. '70 4V = 62.8 + 17 = 79.8 cc = |

|10.01:1 compression ratio. |

72…..11.01

73…..10.87

74…..10.74

75…..10.61

76…..10.48

77…..10.36

78…..10.24

79…..10.12

80…..10.01

81……9.90

82……9.79

83……9.68

84……9.58

85……9.48

86……9.38

87……9.28

88……9.19

89……9.10

90……9.01

91……8.92

92……8.83

93……8.75

94……8.67

95……8.58

96……8.51

97……8.43

98……8.35

99……8.28

100…..8.21

101…..8.13

102…..8.06

103…..8.00

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download