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Discussion Starter #1 (Edited)
Question 1: is there any way to determine compresssion ratio from compression measurements?

Question 2: what is the usual new compression for a NA?

Sam
 

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Question 1: is there any way to determine compresssion ratio from compression measurements?

Question 2: what is the usual new compression for a NA?

Sam

2,384 cc 2.4 liters in-line 4 front engine with 88 mm bore, 98 mm stroke, 10.4 compression ratio, double overhead cam, variable valve timing/camshaft and four valves per cylinder LE5
 

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All thaf info of course wont help if your dojng a compression check.

So your question OP is a little confusing.
 

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Discussion Starter #4
Thank you. You almost won the jackpot, you got one of two. I now need to know what a typical spark plug hole compression check should read.
 

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Thank you. You almost won the jackpot, you got one of two. I now need to know what a typical spark plug hole compression check should read.
According to my research the 2.4L motor in the Sky NA should have a cylinder compression in the 205-245 psi range. No cylinder should read below 100psi. It is important that you do the testing procedure correctly to get an accurate reading. Below is a link with an example on how to do this:

How To A Cylinder Compression Test
 

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Discussion Starter #6
Saturn Sky Dude: Your the man. Now comes the jackpot question. Is there any way to determine the compression ratio from cylinder compression and what we know about the rest of the engine?

It would seem that ambient of 14.7 times 10.4 would come out somewhere in the 150 range. How do we get to the 205+ range?
 

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You posted this :

Thank you. You almost won the jackpot, you got one of two. I now need to know what a typical spark plug hole compression check should read.
I answered your question and then you posted this:

Saturn Sky Dude: Your the man. Now comes the jackpot question. Is there any way to determine the compression ratio from cylinder compression and what we know about the rest of the engine?

I answered two out of two questions and, according to your post, that means I won the jackpot.....your not gonna change the rules all the sudden are you ???
 

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Discussion Starter #8
DUDE: ( as we CA surfers say) You have won the prelim.... now for the Jackpot...

Why don't the numbers work?

By the way, nice bits on measuring the psi.
 

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From a Chemical engineer here's why the numbers don't work. When you compress any gas it heats up. Starting with 60F air at atmospheric pressure of 14.7 psia. Compress the gas with absolutely no cooling by cylinder walls, piston, and cylinder head. The theoretical ending temperature for compression ratio of 10.4 is 867F. The ending pressure would be 375 psig.

Of course none of this happens in a real life cold cranking test. Rings leak, valves leak, cylinder walls cool the air, etc. A compression test is usually just a comparison between the cylinders to see if one is substantially lower than the rest.
 

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I did a compression test on a le5 long ago and they were all 155ish.

Wrong section.;)
He has a stroked 2.0 to 2.4 so "technically" right section, anyway what's up with the build? ;)
 

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You will never get an exact prediction of dynamic compression readings from a static compression ratio.

You can come closer using this sort of calculator:

United Engine & Machine Co. Incorporated
 

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LNF according to my service manual is 140min- 175max psi.
 

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You may want to read up a bit on some of this ,there is a dry test as well as a wet compression test.All the info above is correct as far as what your engine pistons are you should be able to look all that up .Now if you are getting some erogenous readings then that would be a totally different question as to what is going on.
 

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if you are getting some erogenous readings then that would be a totally different question as to what is going on.
If he is getting erogenous anything, he would be working on something other than a car...... :devil:
 
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