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#1
05-04-2008, 12:15 PM
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Compression Ratio
Hello all,
i have a 70 lemans sport conv. with its 350 2bbl about to get rebuilt. the heads are #11's and are 73cc's i think. i am trying to find out( without pulling the old heads yet) if the pistons have valve releifs(i don't think so) and if so how many cc's. also what was the stock head gasket thickness? Im trying to calculate my CR and i've read its a 8.8 but my calculations are giving me 9.32. im using 3.875 bore-3.75 stroke-73cc heads-i put a gasket thickness of .05-a deck height of .023 and 0 cc's-/+ via dome of vavle releif. What's going wrong? the calc im using is http://www.thepontiactransampage.com/compcalc.html Thanks |
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#2
05-04-2008, 01:19 PM
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IF you use -8 cc for valve reliefs and .041 for a gasket thickness your compression comes out at about 8.75:1, which sounds about right. Most Pontiac stock pistons have 4 valve reliefs with a volume of 6 - 8 cc.
FWIW, Stewart
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1976 TA, nose converted to 1970 style, 406, ported #13 Heads, '70 iron intake without crossovers, Q-Jet - Cliff style, RARE OS manifolds, Pypes duals w/crossflow, UD 230/238 custom HR 4/7 swap cam with solid roller lifters  , Hydro-Boost 4-wheel discs, 4 Speed, 3.23 posi.“Nothing in life is so exhilarating as to be shot at without result.” - Winston Churchill |
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