I also computed as CR as 8.3:1 using:
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'Total swept volume' divided by 'compressed volume'. Total swept volume was 930cc and compressed volume was 112cc. 930/112=8.3
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Total swept volume is volume of the cylinder plus volume in the combustion chamber, head gasket, valve reliefs and deck height. I assumed the following: (i) heads had never been milled; (ii)no volume above top piston ring; (iii)head gasket was .042 crushed=5cc; (iv) deck height was -.023=5cc;(v) no valve job on heads; (vi) engine had not been bored
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Compressed Volume=112cc:
91cc for combsution chamber
10cc for head gasket
6cc stock valve reliefs
5cc -.023 deck height
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Total swept volume calculation
3.14(5.2324 * 5.2324)* 9.525 + (compressed vol)
3.14(27.3780)* 9.525 + (compressed vol)
85.966 * 9.525 + (compressed vol)
818.835 + (compressed vol)
818.835 + 112
930.835
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930.835 divided by 112 = 8.3
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Notes,
(i) 3.14 is PIE (greek symbol not on PC keyboard).
(ii) inches were converted into metric using 1"=2.54cm. (ie. bore radius of 2.06 inches = 5.2324cm, and stroke of 3.75" = 9.525cm)
(iii) CR could vary if assumptions are incorrect and/or cc of head is not 91cc. I have read some people saying the 6x-4 is 94cc. Other variables like deck height, head gasket, valve reliefs will also affect the CR.
(iv) I used HO Racing's 'Pontiac Heavy Duty Parts and Specs' as a reference.
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