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Old 12-14-2004, 03:46 PM
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compression ratio.

Hi everyone, I got my water in oil situation fixed. finallly changed intake gasket to a Victor gasket and all is good. Thank you to everyone here on the board who put in their suggestions.

I have a questions about my compression ratio. I just need a ballpark figure. This guy says i have around 8.5:1 but I think its higher than that. My guess is about 9.5:1.

Stock 350 block
flat top pistons (not sure on cc's)
70cc heads
felpro gasket. the one that comes in the kit... .039?
cam specs are 224 int/exh duration. .470 lift, 110 sep.


He says I should change out the fel pros for a GM Shim gasket.

How much will this help me? Is it worth it?
about how much more power/milage will it give me?

I did a PSI test on all cylinders, they were all 150 psi or very close. Is this about right? he says I should be in the 180 range. but as i was reading earlier doesn a narrower lope sep such as 110 bleed off most of the pressure?

Thanks guys

Kyle

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Old 12-14-2004, 09:41 PM
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I ran your set up with 6cc valve reliefs and got a ball park of 9.45:1 with a plain flat top that is 10:1 but im sure you have the reliefs. If your reliefs are 10cc then you have 9:1.


The reason you need a thinner gasket is quench. That is the distance from the top (flat part) of your piston to the flat back of the bottom of the head. So if you have a stock set up with a piston .025 in the hole and a gasket that is .041 between the head you add those two numbers .025 + .041 = .066 which is too much quench. You want it to be the the area of .04 to .055 this all helps fuel and air mix better and allows for a helping hand against detenation.
He is correct.... you have two choices.

1. Have the block decked stock block is 9.025 high which im most stock cases means your pistons sits .025 in the hole. If it is deck you will have 9" as a deck hight and thus can use the .041 gasket and be done.

2. Steel shim which are very thin .015 P/N 1094 from Fel-Pro get a sealer for them such as THIS and make sure the block and head decks are very smooth and flat. .015+.025=.04 which is prefect.


Good Luck,
Chris
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Old 12-15-2004, 12:22 AM
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Here is the KB compression calculator:
http://www.kb-silvolite.com/temp/calc.php
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Old 12-15-2004, 01:14 AM
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Thanks for the responses.

My pistons do have reliefs on them. 4 on each.

Will running this much quench area hurt my motor at all? or just rob me of power?

I dont really want to do a tear down of the cyinder heads, since I just replaced the intake gasket twice since the rebuild. And it is my daily driver.

If I have to I will, but is it necessary?
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Old 12-15-2004, 03:43 AM
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This is a neat article, easy to understand, if you understand what you´ve got it is easier to contemplate the right changes.
http://www.carcraft.com/techarticles/982/index.html
You could have the heads skimmed to be able to use a reasonable thickness gasket, Fel Pro does have a few.
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Old 12-15-2004, 08:55 AM
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If your car runs good now with out detonation then I woudn't worry about the piston to head clearance.

CR guessing around 9-9.5.
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Old 12-15-2004, 10:51 AM
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It runs ok, but It still has tuning issues. anyone around central california are want to make a few bucks? tuning a Holley??
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Old 12-15-2004, 09:03 PM
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Quote:
Originally posted by malc
This is a neat article, easy to understand, if you understand what you´ve got it is easier to contemplate the right changes.
http://www.carcraft.com/techarticles/982/index.html
You could have the heads skimmed to be able to use a reasonable thickness gasket, Fel Pro does have a few.
Milling the heads won't help the quench any. You have to mill the deck surface.
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Old 12-15-2004, 10:48 PM
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Malc,
that is a great article!!!Easy to read and understand!!!!BM
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Old 12-16-2004, 09:27 AM
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More calculators

This site also has a number of good calculators, plus good info on dynamic compression ratio.

If your dynamic (running) compression is too low, you can increase it somewhat by using a cam that closes theintake valve sooner, trapping more compression pressure. You could also advance the cam to get the same effect. Just be careful of piston to valve clearance.

This link has the info
http://www.smokemup.com/auto_math/index.php
http://cochise.uia.net/pkelley2/index.html
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