Pontiac 6X ID

500804 large chamber measures 3.630 at point A

500801 small chamber measures 3.212cast #: 76 GM8, 78 GM4, 78 GM7 I have found to be large chamber, cast#: 76 GM3, 77 GM1 to be small

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Point B is quick junkyard test: that little none machined area is almost machined and sometimes is on the small chamber. The large chamber is well indented.

494331

73-74 455 exc. SD

4X

114cc

494332

73-74 400

4X

110cc

494333

73-74 400

4X

110cc

494334

73-74 400 2BC

?

?

494335

73-74 400

4C

?

494336

73-74 350 2BC

?

?

494337

73-74 350 Calif

4C

?

500801

75-79 350/400

6X

96cc

500802

75-76 455

6H

124cc

500803

75-?

?

?

500804

75-78 400

6X

110cc

497702

75-? 350

?

?

495345

75-76? 455

?

?

487076

73 350 Press Studs

?

?

 

Cylinder Head Chamber Volume, cc's

50

55

60

65

70

75

80

85

90

95

100

105

110

115

303

9.35

9.18

8.67

8.23

7.83

7.47

7.15

6.86

6.60

6.36

6.14

5.93

5.74

5.57

326

10.00

9.78

9.25

8.77

8.34

7.95

7.61

7.30

7.02

6.76

6.52

6.30

6.10

5.91

354*

11.23

10.55

9.97

9.45

8.98

8.57

8.19

7.85

7.54

7.26

7.00

6.77

6.55

6.34

366

11.55

10.86

10.25

9.71

9.23

8.80

8.42

8.07

7.75

7.46

7.19

6.95

6.72

6.51

389

12.20

11.48

10.83

10.26

9.75

9.30

8.89

8.51

8.18

7.87

7.58

7.32

7.08

6.86

400

12.53

11.77

11.11

10.52

10.00

9.52

9.10

8.72

8.37

8.06

7.77

7.50

7.25

7.02

411#

12.86

12.08

11.40

10.79

10.26

9.77

9.34

8.95

8.59

8.27

7.97

7.69

7.44

7.19

421

13.15

12.36

11.65

11.03

10.48

10.00

9.54

9.14

8.77

8.44

8.13

7.85

7.59

7.34

428

13.31

12.50

11.79

11.16

10.60

10.10

9.65

9.25

8.87

8.53

8.22

7.94

7.67

7.42

439%

13.54

12.71

11.99

11.35

10.78

10.27

9.81

9.40

9.02

8.67

8.36

8.06

7.79

7.60

455

14.15

13.28

12.52

11.85

11.26

10.72

10.24

9.81

9.41

9.05

8.71

8.41

8.13

7.86

469~

14.52

13.63

12.85

12.16

11.55

11.00

10.50

10.06

9.65

9.28

8.93

8.62

8.33

8.06

#400 bored .060"           %428 bored .060"          ~455 bored .060"           *Actual displacement of 350.

The above figures assume 10 cc for .042" (crushed) head gasket, 6 cc valve reliefs for 400 stock pistons, 5 cc for -. 023" deck height on 4.120" bore and flat top pistons (no dome). To correct for pop-up pistons, subtract dome volume from chamber volume. To correct for deep valve reliefs, add relief volume to chamber volume. Note that stock claimed compression ratio is usually 0.50 more than actual compression ratio.

 

 

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