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Old 07-09-2006, 07:29 AM
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How can I confirm Compression Ratio on 406SBC?

I bought a rebuilt 406 without knowing what's inside.I started it up for the first time last week and I am sorta dissapointed in performance.I am trying to figure my CR without pulling the heads and measuring the cc's.I it has full dished pistons I know this because i looked at them through the spark plug holes before i installed the engine.If the World Product Sportsman heads are 76cc's my CR is too low.Are there any numbers on the heads telling me if they are 76 or what i hope 64cc's?If not are they any other way to tell CR without pulling heads?
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Old 07-09-2006, 08:37 AM
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Compression is a mechanical calculation and needs the cc of the combustion chamber etrc. Without an expensive testing unit it is not easy to derive compression ratio on an assembled engine. But even low compression engines can make strong power,it could be something like cam timing or ignition curve. I think you should be able to determine the cc of the heads with a number on it and the listing for the heads.
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Old 07-23-2006, 07:27 AM
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I was told their were no casting numbers on the heads to identify 64 or 72cc's.I checked the cranking compression yesterday and it was 130PSI.Does this tell me anything?
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Old 07-23-2006, 08:05 AM
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Absolutely...

nothing...

Part of the problem is you've no idea what the duration
of the cam is, I have a 10.5:1 2.0L Pinto that has a long
duration cam in it, and makes 135psi doing a compression
test...

K
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