I just went in one of the compression calculators and it is showing 12.09:1 !!
I used the following:
head 60cc
stroke 3.622
bore 4.0
head gasket .045
Deck height -.01 (piston pop out)

Is this too high??? should I run a thicker head gasket or will that cause other problems? Am I calculating this wrong?

thanks for the info!

 

are you forgetting dish on the piston? how about head gasket bore? you show thickness but not bore. if you are sure its an LQ9 then there is no one, but otherwise the only other calculation that some people leave out is the area from the top ring to the top of the piston, but that doesnt change very much. using a thicker head gasket will not change much on the SCR either, but you may want to look at your DCR and see what it comes out to.

 

Its an LQ9 out of an 06 Escalade. The calculator didn't ask me about the bore on the gasket. Pistons are flat. Still haven't picked a cam yet, since I am not sure what will fit and not have piston to valve issues...... I tried some thicker gaskets in the calculator and it didn't make much of a difference in the static compression....

 

you should look at a different calculator then. it factors in.

 

went on a new calculator and used 4.030 for the gasket bore.
dropped down to 12.07

If I go with a .051 gasket thickness it dropps to 11.87:1

If i happen to not have pop out of .1 (still need to measure) and have .008, then it drops to 11.80:1.

Is this still too high? Do I run into any issues going to the thicker head gasket?

thanks

 

"If i happen to not have pop out of .1 "

think the stock piston will be .100 out of the hole.
My stocker is .007.
Be careful when measuring. Take the measurement at the pin c/l. Otherwise, the piston may be cocked in the bore, giving an inaccurate dimension..

 

A compression check will tell all for the most part .

How deep are the valve reliefs in the pistons ? Valve relief can be added to the head cc size

I just burnt #7 piston because my compression was to high .

I was running a 66cc head on the Lq9 with 0.00 out of the hole , .043 gasket compressed with 6cc valve reliefs with a 4.030 bore and 4" stroke .

Do a compression check and see how high yours is because the cam your using might bleed off some of your compression .

I was sitting at 225-227 cranking compression which is a little to high for pump gas .

What are your cam specs ???

 

I would talk to your tuner and also look at the fuel you are going to use. If you can handle the higher CR, then there is no reason to not go with it. Also with a more aggressive cam you will see your DCR go down, which is the actual operating compression ratio of the engine. The SCR will give you the base line.

^ and I think you have compression ratio confused with compression test. they are not related like you think they are.

 

[QUOTE=Old Geezer;12543782]"If i happen to not have pop out of .1 "

oops fat fingers..... I meant .01 out of the hole.

 

I don't have a cam spec'd yet. I still need to figure out the piston to valve clearance. this is a STOCK Lq9 so there are no vavle releifs. My 383 was at 11.75 with a 236/236 cam .550 /110. Never had detonation problems and road raced the crap out of that motor.

 

Your compression is ~ 11.46 with stock MLS gaskets

 

True , they are not truely related but you can draw an idea of where you stand .

If you get 225-230 like i did , the cam is not bleeding off compression , which is still ok if you run higher octane fuels , but i wasnt , i was still thinking i had 68cc heads .

My last build would have lasted a long time if i was running race gas in it , but my head were shaved/cleaned up more than was stated so the higher compression killed #7 and was working on #5 .

With 1.5 bad pistons the car still ran fine and didnt show signs of anything wrong and ran an 11.15@122 , i just tore it down to check things out before spraying 2 kits on it and now im glad i did .

 

who's is?

 

Yours

 

With a gasket bore of 4.03 and with everything else the same as above you are looking at 11.44:1 compression and a total volume of 71.47CC if you go with an MLS with a thickness of .054 you'll drop to 11.17:1 compression.

 

GM Gaskets are also much cheaper than a comparative Cometic.

 

How come your numbers are so much different than what I got from the calculator? Not doubting you, just trying to learn and understand.
At least these numbers are a little safer. I always only run 93 oct gas in my car. I generally use bp or mobile or shell.

I think I would rather have the 11.44 compression vs 11.17??? wouldn't it make more power or is it not worth the added risk?

I may spray this with a 100 shot once in a while. Stock gakets ok?

thanks

 

From what i understand the best target number is 11.8:1 compression for our motors and 93 octane for proper quench .

11.44:1 will be just fine .

 

Where I think you went wrong in the calculator you had to add 0 for piston because it is a flat top piston not a dome. If you are going to run 11:1 compression nothing below 91 and 11.5:1 I would not do anything less than 93 personal preference. Running the 11.44:1 is better for hp and for N2O also depending on the cam you need to make sure that your cam is a N2O friendly. While 100 N2O is considered a small shot I have been advised never run dry or wet with anything less than 100 octane if its bigger than a 50 shot due to detonation. This is from the guy who does all the N2O set ups in my town. The other thing to remeber LS engines have a nasty little habit of leaning out Cylinder #7. Some of the best have blown their engines with this occurance. Stock gaskets are fine. The one thing that you have to make sure is that all your torque specs are correct when installing your heads.

Good Luck

 

Is the calculator you are using on line?
I made sure i put in a negative value for the piston protruding out of the deck, calclulated the volume of the head gasket and still can't get 11.4

I got this using this calculator and these numbers:

http://www.ajdesigner.com/phpengine/...sion_ratio.php
Conversions:
BORE = 4 inch = 4 inch
STROKE = 3.622 inch = 3.622 inch
CCV = 60 centimeter^3 = 3.6614246456839 inch^3
HGV = .5740 inch^3 = 0.574 inch^3
PDV = -.125664 inch^3 = -0.125664 inch^3

Solution:
compression ratio (CR) = 12.074976068935

It is lower if I use PDV as a positive number.... but that would mean that it is in the hole. Like I said, not doubting, just trying to understand.

thanks