01-11-2009, 06:14 PM
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Senior Club Cobra Member
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Join Date: Jan 1999
Location: MARKSVILLE,LA.,,
Posts: 3,235
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Not Ranked
Compression ratio and cranking compression are two different animals.........
The cranking compression has a lot to do with the camshaft profile, probably more so than anyhting else...(assuming a good ring seal and good valve seal) the amount of overlap in the profile has a ton to do with cranking compression....
My 10.5 to 1, 351-W cranks out at about 125 psi, but my camshaft has a lot of overlap and at those low cranking speeds, bleeds off the compression as it is designed to do. by contrast, I checked a bone stock 351-W and it's cranking compression was 145 psi!!!!!!!!!!!
doing a cranking compression test is a good way to check for ring sealing and valve seat wear/sealing, not a good way to determine overall compression ratio...
David
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DAVID GAGNARD
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