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Old 06-14-2004, 06:04 PM
Chucksdart Chucksdart is offline
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Question What's my compression ratio?

Hey guys, I need to know how to figure out my comp. ratio. I have a 1970 340 bored .060 . It has trw flat top forged pistons jegs # L2316F60. Felpro head gaskets, 915 "J" heads. Can someone tell me how to do the math? Thanks!
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Old 06-14-2004, 07:42 PM
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http://mopartech.hamcar.info/phpBB2/viewforum.php?f=13

There's a link to a page I wrote that will tell you how to check your CR ratio. You'll have to get a machine shop to CC your heads if you don't know what they are, cause they all vary.
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Old 06-16-2004, 02:53 PM
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Just looking through my Federal Mogul Catalogue and it lists general compression ratios, of course these will vary according to your actual chamber volume.

Head cc 63 65 68.4 71

C/R 10.5 10.25 9.86 9.59


These are for your L2316F .060 pistons.

Just so you know when you do your calculation the valve relief volume on your pistons is -7cc's.
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Old 06-16-2004, 03:51 PM
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try this site.

http://www.rosspistons.com/calculator.php
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Old 06-16-2004, 03:59 PM
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try this site.

http://www.rosspistons.com/calculator.php
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Old 06-16-2004, 07:15 PM
Chucksdart Chucksdart is offline
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Thanks fellas, Info was very helpful. I should have cc'd the heads before puttin them on (DUH!) Oh well, the info gives me a pretty good idea. I didn't know the heads could vary that much. Well, when they come off I will do it for sure. Thanks again
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Old 06-16-2004, 11:06 PM
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If I remember right the J heads were 68.4 cc if they haven't been planed down. I also read for every .010 planed off of them subtract 3-4 ccs. I don't know how accurate this is but I think it's close. Also the felpro's have a compressed thickness of .039. Not sure what that converts too in cc.
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Old 06-16-2004, 11:13 PM
Chucksdart Chucksdart is offline
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What is the deck heighth on a stock block that has not been decked?
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Old 06-17-2004, 02:04 AM
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I believe it it 9.60" from the crank centerline to the top of the deck, Chucksdart.
Or are you talking about piston to deck height clearance? that is going to vary from piston to piston as they have different compression heights and some 340 pistons have a negative clearance, that is, they come out of the bore a few thousanths.
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