comp ratio, ran a calc?

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comp ratio, ran a calc?

I have been getting everthing figured out for my build and have been real busy with work. I ran my numbers into a comprssion calc and came out with 12.2.1?

I have a stock spec 357 build (40 over bore, 3.48 stock crank). The crank has been turned .020, .027 headgasket, .014 milled off the heads (94 casting) no decking or anything done to the block aside the .040 bore. The piston is just as far in the hole as stock.

I thought i would be around 11.6.1 or 11.7.1? any help

Last edited by slomarao; Oct 10, 2010 at 02:05 PM.

Oct 10, 2010 | 01:41 PM

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What piston relief...

Oct 10, 2010 | 01:52 PM

kgkern01

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Assuming about 5cc volume piston reliefs, stock deck height is usually around .025", you need to know your head cc's. I assume around 53cc being milled .014". You also need to know the bore size on the head gaskets, what gaskets are .027" thick? I know the Impala gaskets are .029" and 4.1" bore and the 1074 Felpro's are .026" thick with 4.125" bore.
So using the folowing:
'assumed' 5.0 cc valve relief volume for pistons
.027" thick, 4.1" bore head gasket
3.48" stroke
.025" deck height
53cc chamber volume

I get an 11.58:1 SCR

Oct 10, 2010 | 01:56 PM

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Quote:

Originally Posted by kgkern01

I always use .034 deck height. Seen a bunch of people say that's where theirs measured. Did you use a 4.060 bore in your calculations?

Oct 10, 2010 | 01:57 PM

speed_demon24

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Quote:

Originally Posted by kgkern01

1074 Felpro's are .026" thick with 4.125" bore.

Uh....

Last edited by speed_demon24; Oct 10, 2010 at 02:14 PM.

Oct 10, 2010 | 02:02 PM

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the custom gaskets are 60 over so they dont go into the chamber

Oct 10, 2010 | 02:07 PM

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Quote:

Originally Posted by slomarao

the custom gaskets are 60 over so they dont go into the chamber

Uhhh yeah. Whats your point

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Oct 10, 2010 | 03:21 PM

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LT1 gasket bore sizes are usually 4.100 or 4.125. You shouldn't need a "custom gasket" to prevent them from entering the chamber. Are we all talking about the same thing here?

Oct 10, 2010 | 10:01 PM

#10

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I was on the phone with a summit racing tech, he said this is the way to go for my setup

Oct 10, 2010 | 11:25 PM

#11

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Quote:

Originally Posted by slomarao

I was on the phone with a summit racing tech, he said this is the way to go for my setup

Lol..

Oct 11, 2010 | 06:48 AM

#12

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Oh boy. Have you tried consulting an engine builder, and not a part-time parts guy at an internet wholesaler?

Oct 11, 2010 | 01:11 PM

#13

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thanks for your help guys, really, glad i posted the question

Oct 11, 2010 | 01:34 PM

#14

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We're just trying to clarify what you've got going on that's all. Summit techs don't exactly have the best track record for providing accurate and relevant info in a performance build.

Oct 11, 2010 | 02:51 PM

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Puck

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Your CR will be ~11.4-11.5.

Oct 11, 2010 | 08:43 PM

#16

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Quote:

Originally Posted by Puck

Your CR will be ~11.4-11.5.

THANKS, that is all i was looking for.

Oct 11, 2010 | 08:57 PM

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speed_demon24

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Quote:

Originally Posted by gregrob

I always use .034 deck height. Seen a bunch of people say that's where theirs measured. Did you use a 4.060 bore in your calculations?

Mine was .015 or .020 i think. It's been awhile but I came up with 11.4-11.5 with a .029 gasket and 53cc chambers.

Oct 11, 2010 | 10:15 PM

#18

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close enough, Ill call it 11.6.1 cuz i have a 027 gasket

Oct 12, 2010 | 04:27 AM

#19