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Compression ratios |
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rmatt684 
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Joined: Jan/11/2015 Location: Whiteland,In. Status: Offline Points: 57 |
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 Topic: Compression ratiosPosted: Aug/17/2018 at 7:22pm |
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1968 343 H.C. V-8 , I did a compression this spring and all cylinders were 150. Now # 1 is 180, 2,3, 4,6 & 7 are 150, #5 is 210 ( checked it twice )# 8 is 180. Any thoughts why #1, #8 and # 5 are so different ? No changes to the engine this year.
Thanks for the help.
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PROSTOCKTOM
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Joined: Jun/20/2010 Location: Indiana Status: Offline Points: 2458 |
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Posted: Aug/17/2018 at 7:35pm |
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There are a lot of tolerance differences within an engine. That is why race engines are blueprinted. You could have a longer or shorter piston mixed with a longer or shorter rod. OEM cast piston can vary a lot from batch to batch. Cam lobes can also be off from lobe to lobe. Cylinders/ rings can differ, quality of valve job. If you were to take it apart and measure it all the parts carefully you could probably get your answer.
Tom
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vinny
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Posted: Aug/17/2018 at 8:48pm |
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I have never seen it but have heard that if compression increases it must be due to carbon build up.
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rmatt684
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Posted: Aug/17/2018 at 9:59pm |
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Thanks tom but this is something that has happened since the spring of this year.
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PROSTOCKTOM
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Posted: Aug/17/2018 at 10:52pm |
Then it's either valve job or ring sealing. How many miles/ years are on the engine? Tom
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rmatt684
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Posted: Aug/18/2018 at 6:24am |
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Tom, Think your right about it's time to take the heads off and see what is going on.
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vinny
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Posted: Aug/18/2018 at 10:44am |
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The way I read it his problem is too much compression so how can rings or valves be the cause? Decreased volume above the piston can be the only cause.
I'd try some carb-out product before taking it apart. Some people swear by pouring water down the carb at fast idle but I have yet to try it myself.
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Boris Badanov
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Posted: Aug/18/2018 at 10:51am |
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If they were all 150 till now it's
Oil or coolant collecting in the affected cylinders, maybe gasoline... It's that simple. |
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Gremlin Dreams
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purple72Gremlin
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Posted: Aug/18/2018 at 11:07am |
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Is it using oil?... I know what your compression readings are saying. Id do a leakdown test..IMHO that will tell you more about the cylinders condition.
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vinny
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Posted: Aug/18/2018 at 11:33am |
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Cylinder condition is good. I think Boris said it best.
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rmatt684 wrote: