formula for figuring compression?? - PowerStrokeNation : Ford Powerstroke Diesel Forum
 
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post #1 of 7 (permalink) Old 02-15-2009, 03:21 AM Thread Starter
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formula for figuring compression??

Hey im just curious as to how exactly you go about figuring the compression ratio in a motor? i had my pistons worked over a little and would like to figure what im at. Do you have to figure the CCs of the bowl then use a formula to convert that to your compression ratio? Thanks

Robert


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post #2 of 7 (permalink) Old 02-15-2009, 03:28 AM
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Re: formula for figuring compression??

http://www.rbracing-rsr.com/compstaticcalc.html

Second one on a google search.

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post #3 of 7 (permalink) Old 02-15-2009, 04:04 AM Thread Starter
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Re: formula for figuring compression??

thanks im right at about 16.5:1 ratio


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post #4 of 7 (permalink) Old 02-15-2009, 04:35 AM
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Re: formula for figuring compression??

That should be just about perfect, it'll still start okay in the winter
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post #5 of 7 (permalink) Old 02-15-2009, 05:12 AM
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Re: formula for figuring compression??

my 15:1's start just fine outside, cold in the winter. starts just as quick as stock, but the white smoke, err.

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post #6 of 7 (permalink) Old 02-15-2009, 07:52 AM
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Re: formula for figuring compression??

Miscalculation or an omission of the valve relief volume in the head, and the area above the top ring but below the crown can cause your numbers to be off by a full compression point. Those online calculators only give you part of the picture - the only way to truly calculate compression is by the swept volume vs compressed volume calculations involving actually taking cc measurements of the bowl, valve reliefs, calculating gasket volume, etc...

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post #7 of 7 (permalink) Old 02-16-2009, 01:23 AM Thread Starter
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Re: formula for figuring compression??

I should be pretty close then, i found the cc in the bowls and took mesurements before i put it together, wrote it down on some paper i just didnt know how to calculate that into the compression ratio.

Robert


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Terminator HPOS
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