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I have a L96 out of 2012 2500 which is being bored out to a 6.2 and I need help determining my compression ratio to see if I need to change anything. I have tried a couple of compression ratio calculator but I want to put it out here just incase I’m missing something. I’m using the stock rods and going with summit racing pistons. Plan is to run NA for little bit and then add a supercharger. Below is the all the specs I can think of to calculate the ratio. Please ask if there is anything else missing. Thank you
Bore size: 4.065
stroke: 3.622
(823 heads)head chamber CC: 70cc
ls7 head gaskets: bore size 4.150 and thickness .075 Piston Style:
Dish, with two valve reliefs
Compression Height (in.):
1.326 in.
Piston Head Volume (cc):
+12.00cc
Last edited by Ranjodh Singh; 05-07-2021 at 01:02 AM.
Using Summit's compression calculator (available online to anyone), your CR is 8.87:1. VERY low.
Are you sure about the .075 head gasket?? Stock thickness is .052.
But even with that it would still be a low 9.28:1.
No LS engine ever came with less than 9.5:1.
Using Summit's compression calculator (available online to anyone), your CR is 8.87:1. VERY low.
Are you sure about the .075 head gasket?? Stock thickness is .052.
But even with that it would still be a low 9.28:1.
No LS engine ever came with less than 9.5:1.
You need to verify the pistons in the block first.
if they are aftermarket replacement pistons they might sit below the deck which will effect the compression ratio.
You need to verify the pistons in the block first.
if they are aftermarket replacement pistons they might sit below the deck which will effect the compression ratio.
I believe this piston height of 1.326 is close to the height of the stock piston.
You need to verify the pistons in the block first.
if they are aftermarket replacement pistons they might sit below the deck which will effect the compression ratio.
That's a very good point. Our Pro LS pistons sit .005" in the hole. We do this because some factory blocks have been recorded close to 9.230" deck height. That's quite a bit off from the 9.240" they are supposed to be. We also know our customers like to mill the heads and deck the blocks. Being a little in the hole and dropping .1 of compression is basically inconsequential. On the other hand, hitting the cylinder head is very consequential.
OP,
Using our calculator and your specs you would be around 8.78:1. That is really low. Going with a .040" head gasket would put you right around 9.42:1. That gets you real close to your 9.5:1 target and tightens quench up to .045". This is quite a bit better than the .080" you'd see with the .075" head gaskets you described. Tightening the quench will help provide a cleaner more efficient combustion cycle. It will also help reduce the chance of engine knock.
Here's what our compression calculator would look like using .040" head gaskets. We use 70cc for 823 heads per the research we've done on these L96 LS engines. We've compiled quite a bit of info on Gen III/IV engines. You can view charts for all of the Gen III/IV engines in our Identify Chevy LS Engines by VIN/RPO code article.
That's a very good point. Our Pro LS pistons sit .005" in the hole. We do this because some factory blocks have been recorded close to 9.230" deck height. That's quite a bit off from the 9.240" they are supposed to be. We also know our customers like to mill the heads and deck the blocks. Being a little in the hole and dropping .1 of compression is basically inconsequential. On the other hand, hitting the cylinder head is very consequential.
OP,
Using our calculator and your specs you would be around 8.78:1. That is really low. Going with a .040" head gasket would put you right around 9.42:1. That gets you real close to your 9.5:1 target and tightens quench up to .045". This is quite a bit better than the .080" you'd see with the .075" head gaskets you described. Tightening the quench will help provide a cleaner more efficient combustion cycle. It will also help reduce the chance of engine knock.
Here's what our compression calculator would look like using .040" head gaskets. We use 70cc for 823 heads per the research we've done on these L96 LS engines. We've compiled quite a bit of info on Gen III/IV engines. You can view charts for all of the Gen III/IV engines in our Identify Chevy LS Engines by VIN/RPO code article.
is it safe to run the motor at 9:5:1 na for a while before I add on the supercharger?
05-07-2021, 12:52 AM
Compression ratio help! 
