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Compression numbers

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Old 11-01-2005, 04:52 PM
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1990mustanggt
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Default Compression numbers

Does anybody know how to calculate compression ratios. Like lets say you have 190 psi in a cylinder, how do you find out what that is? You now 9.5:1 so on and so on. I found one place that can give estimates by inputing certian numbers, but I'm not exactly sure about all my measurements. I just want to be able to say, "I have this much psi on the cylinder. What is the ratio?" Here is what I came up with on one site.

Compression Ratio Calculator



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Bore Size: 4.030"
Piston Clearance: 0.004" Took a guess on this one

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Stroke: 3.40"
Cylinder Head Chamber Volume: 61 cc

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Deck Height: -0.010" Took a guess on these two
Piston Dome/Dish Volume: 2.3 cc

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Head Gasket Bore Size: 4.10" And on these two
Head Gasket Thickness: 0.041"

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Engine Size = 347.64 cid



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Cylinder Volume = 712.10 cc
Gasket Volume = 8.87 cc
Deck Volume = 2.09 cc

Total Volume = 786.37 cc
Compressed Volume = 74.26 cc


Compression Ratio = 10.59:1

I tried to do a search but found nothing.


[IMG]local://upfiles/10184/F918E32023DA4AE19FAF9E87307EC74A.jpg[/IMG]

[IMG]local://upfiles/10184/F9B51F3732C342D28AC32DD2E394387B.jpg[/IMG]
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Old 11-01-2005, 05:44 PM
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1990mustanggt
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Default RE: Compression numbers

Any takers on this one. It has me stumped on where to find it at on the NET.
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Old 11-01-2005, 07:37 PM
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JD1969
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Default RE: Compression numbers

It's because you can't calculate the static compression using the psi numbers from the gauge, things like cam overlap and leak down will affect the reading on the gauge.
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