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Old 02-18-2011, 06:23 PM
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Compression ratio math

283 v8 build with vortecs-

stroke is 3"
chamber 64cc, but the stock 283 head was 64 cc.
gasket bore 4.000" .027 thick, 5.56cc
pistons .025 under deck 4 cc with 7cc relief, 11cc total

That is 8.15:1 . It might be a lil thin , but 70s compression numbers were in the 7.5-8 range.

305 Vortec swap-

Stroke 3.75"
chamber 62cc, milled .025"
gasket 4.000" .027" thick, 5.56cc total
pistons .020 under with 7cc relief, underdeck total 10.77

That comes to 9.0:1 compression. Good for a heavy truck and regular fuel.

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Old 02-19-2011, 08:24 AM
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The bore and stroke should be clearer.

283 bore 3.87" stroke 3.00
305 bore 3.75" stroke 3.48

Is the math correct?
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Old 09-29-2011, 09:28 PM
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If I understand you correctly, this is a 0.020" over bored 283 (3.895" bore), 3" stroke, 0.025" piston below deck, 7cc valve reliefs, 62cc chambers, 0.027" gasket thickness x 4" gasket bore diameter.

In inches
Enter Bore size: 3.895
Enter Stroke size: 3.00
Enter Head Gasket Bore size: 4.00
Enter Compressed Head Gasket Thickness: 0.027
Enter Combustion Chamber Volume in CC's: 62
Enter Piston Dome Volume in CC's use "-" for Dished Pistons: -7
Enter Piston Deck Clearance If ABOVE deck use "-" : 0.025

Compression Ratio: 8.37:1
Total Volume: 79.44 cc

With a standard bore the CR is 8.30:1
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