Trying to figure comp ratio

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Trying to figure comp ratio

Post  57custom on February 21st 2013, 12:28 pm

I have a 466 with iron cobra jet heads and did not check the compression ratio before assembling it. I would like to have some idea of the ratio now for various reasons. The pistons are speed pro forged with a 12cc dome if that helps. The heads are slightly ported DOOE cobra jet and i am not sure if they have been milled. I suspect not but if they are it was maybe just to true them up. Any help or good guesses would surely be appreciated. I,m thinking around 12.5 to 1. Am I in the ballpark as you can see it is .030 over at 466 cid. Very Happy
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Re: Trying to figure comp ratio

Post  IDT-572 on February 21st 2013, 1:53 pm

Is the piston below the deck and what is your gasket bore and compressed thickness.

If your 0 deck and 72cc chamber and a + 12cc you could be 14:1.
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Re: Trying to figure comp ratio

Post  466cj on February 21st 2013, 3:28 pm

Zero deck, 0.042" gasket, 72cc chamber, +12cc dome = 14.48
Zero deck, 0.042" gasket, 69cc chamber, +12cc dome = 15.05
-0.010" deck, 0.042" gasket, 72cc chamber, +12cc dome = 14.01
-0.010" deck, 0.042" gasket, 69cc chamber, +12cc dome = 14.56

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The piston is down

Post  57custom on February 21st 2013, 5:27 pm

.010 from the top of the block. It I remember right the compression was rated at 11 to 1 when the 429 was new. So you guys are saying that the extra 36 cubic inches and the 12cc dome will raise it that high? WOW if I had realized that I would have milled the tops of the pistons off. Do you think 110 octane will work with this compression ratio? As that is very available close to where I live or should I think about Alcohol? I am already planning on putting a "water meth" injection unit on it. Help me out guys as I sure didn't think it would be this high. This is a tunnel ram engine that I am planning on putting in my fairlane. It already has a pump gas 545 in it now that will end up in another project. This is for a "nostalgic carbs thru the hood" type look for this car. Its a "bucket list" thing for me. Ford iron heads and a flat tappet cam. Smile
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Re: Trying to figure comp ratio

Post  466cj on February 21st 2013, 5:55 pm

Yes you are a solid 14:1. I'd use C-12. Who's 110 are you talking about?

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Re: Trying to figure comp ratio

Post  IDT-572 on February 21st 2013, 6:19 pm

You need to be careful on the cam you select also............... Short timing events could lead to very high cylinder pressure.

You may want to rethink and put flat tops in this deal if your gonna run it on the street and max hp is not your goal.
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Re: Trying to figure comp ratio

Post  the Coug on February 21st 2013, 6:50 pm

http://www.diamondracing.net/tools/
here you go try this if you fill it out right you will get your answer...
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