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Old 04-23-2010, 02:17 AM
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355 sbc compression question

I have some afr heads that are 69cc with 2 different set of dome piston, one set of pistons is 11, the other set of pistons is 12, my block is 0 deck can anyone tell me what type of compression the two would make out to be bacause i dont know how to add that up proper. Thank you for any help that you may have.

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Old 04-23-2010, 03:05 AM
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I use the calculator at www.wallaceracing.com , scroll down the page and click on automotive calculators, you will need a gasket thickness to get an accurate result.

-11cc(dome) was 11.9 to 1, -12cc(dome volume) was 12.1 to 1, both figured with an .041 gasket thickness and zero deck.
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Old 04-23-2010, 07:33 AM
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what is the cc of the piston.

when pistons are rated as 10;1 or 11:1, there is a head combustion size that goes along with that rating. typically they use a zero deck and 64cc for a sbc.

So, do you have any more information about the pistons? a part number would help a lot.
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Old 04-23-2010, 10:10 AM
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no i dont have any more info on the piston i really dont remember which one i use when i built the motor all i remember was 11.1 an 12.1 dome piston

Last edited by Tommy Brown; 04-23-2010 at 10:26 AM.
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Old 04-23-2010, 02:48 PM
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then sorry but unless you're willing to take the heads off and cc the top of the pistons then we really can't help you that much. to be honest between what the manufacturer says it will be and what it actually ends up being at the end of the day when everything is togehter and with all the different part used they can be off as much as 0.5 of a point and sometimes more
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Old 04-23-2010, 06:56 PM
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My previous reply won't help you, I took the info you gave as being the dome volumes. If all you know is that they are 11-1 and 12-1 pistons you will be unable to find out the true compression ratio you have without knowing or measuring the dome volumes.
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Old 04-23-2010, 07:59 PM
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IF the 12:1 pistons were with a 64 cc chamber, a zero deck and a 0.041 composite gasket, the CR w/69cc heads will be ~11.22:1.

With the 11:1 pistons, the 69cc CR will be ~10.34:1.
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Old 04-26-2010, 10:35 AM
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I just found out that they is 12-1 with 64cc heads so that would make it 11 something with the 69cc heads.
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Old 04-26-2010, 11:03 AM
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more than likely yes, but there is no absolute way to tell without pulling the heads off and really finding out what pistons you have in there, getting either the part numbers or measuring the volume of the either dome, dish or valve reliefs
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Old 04-26-2010, 11:26 AM
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Quote:
Originally Posted by Tommy Brown
I just found out that they is 12-1 with 64cc heads so that would make it 11 something with the 69cc heads.
Ya think?? lol
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Old 04-26-2010, 11:30 AM
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No think you cobalt327 an the rest of you guys thats on here for all of your help
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Old 04-26-2010, 11:37 AM
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Quote:
Originally Posted by Tommy Brown
No think you cobalt327 an the rest of you guys thats on here for all of your help
I'm just yanking your chain- and anyway, it is always good to have verification.

Good luck.
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Old 04-26-2010, 11:38 AM
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dont get mad at cobalt, he just gets a little cranky sometimes like the rest of us, if you look at one of his earlier post he stated exactly what you did, i think that might have been the source of his frustration
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Old 04-26-2010, 11:43 AM
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It's cool i just did what my87z said to do an i called the guy who build it an he told me what they were.
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Old 04-26-2010, 12:05 PM
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good stuff, anymore questions
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