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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.
 

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I've never heard of a way to calculate static mechanical
compression ratio from compression pressure readings.

Most engines will be within a range of compression pressure
readings, regardless of static mechanical ratio.

An engine with high mechanical ratios will have longer
duration cams to bleed off compression pressure so
that it falls within a workable range.

An engine with low mechanical ratios will have shorter
duration cams to trap more compression pressure
so, again, it falls within a workable range.
 

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the cam events play into cranking compression big time - no way to infer compression ratio from cranking compression.
 
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