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Old 06-19-2008, 07:22 PM
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CR help

I'm trying to figure out what my compression ratio is without pulling the engine apart. It is a Chevy 350, stock bore & stroke (bore 4", stroke 3.48"), the pistons have 292-00-16-c and H345NP on them, leads me to these Summit link, heads are 354434 305 heads with 60cc chambers, and last but not least- the trouble spot- the head gasket. I can't really make out the lettering on it, but from searching, seems to say "Cortec" and 820312 and 0772, but I can't find anything on that "part number" or numbers...

Any help would be greatly appreciated, if theres any info I can get that might help, please let me know.

Thanks in advance for any help

eazy

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Old 06-19-2008, 08:27 PM
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Assuming a deck clearance of .025" and using a clevite head gasket #5746 with .026", 4.100 I get 10.45:1.
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Old 06-20-2008, 06:49 AM
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Thanks. If anyone has put some numbers into a calculator, feel free to post them up.
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Old 06-20-2008, 07:26 AM
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cylinder= 717cc
piston = 5cc
head cc= 60cc
deck height (assume 0.020")=4cc
head gasket (0.040 or 0.025)= 8.6cc or 5.4cc

With a 0.040" head gasket
(717 + 5 + 60 + 4 + 8.6)/ (5 + 60 + 4 + 8.6) = (717 + 77.6)/ (77.6) = 10.24

With a 0.025" head gasket
(717 + 5 + 60 + 4 + 5.4)/ (5 + 60 + 4 + 5.4) = (717 + 74.4)/ (74.4) = 10.63

Need to measure the deck height to know the cr.
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Old 06-20-2008, 03:48 PM
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Thanks for the info, can I measure deck height with the heads on????? Either way; thanks for the info, a ballpark is better than having no idea.. Just trying to keep somewhat busy until the engine is back in my car........
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Old 06-20-2008, 04:29 PM
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NO, Deck Height is the top of piston to top of block deck surface. If piston is down in the cylinder .025" at TDC that's the deck height.
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Old 06-21-2008, 02:57 AM
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To some people, deck height means the height of the block from the centerline of the main bearing bore to the deck. To eliminate any confusion, I differentiate the two when explaining something on here.
BLOCK DECK HEIGHT distance from the centerline of the main bearing bore to the block deck. (usually 9.025" SBC stock)
PISTON DECK HEIGHT distance from the crown of the piston to the block deck with the piston at top dead center. (usually 0.025"-0.035" SBC stock)
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Old 06-21-2008, 10:05 AM
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Quote:
usually 9.025" SBC stock
Zaklee. There are short deck sbc's too. The stack measurement should reveal something. A machinist given a block to machine to a Zero deck (9.005) could care less where or what you measure.
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Old 06-21-2008, 10:21 AM
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Thanks TechInspector & Stroke, I should have put Piston Deck Height.
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