test.

 

If you take the deck height and use a positive operator and make it +.005 and use .052 as the compressed gasket thickness everything seems to add up right for an LS1. If you use the Piston down bore of -.008 and a .060 head gasket, the LS6 CR is correct. As I see it there are basically 5 variables that need to be considered when computing compression ratio.

1: Head Chamber Volume. Stock is 66.67cc for an LS1 head and 64.43cc for an LS6 head.
2: The stock head gasket bore is 3.910"
3: The stock MLS gasket thickness is .060 compressed and the stock graphite gasket is .052" compressed. That gives a Head Gasket Volume of 11.81cc for an MLS gasket and 10.23cc for a graphite gasket.
4: Deck Volume which is Piston down bore @ TDC. Stock is -.008". That gives a deck volume os -1.57
5: Swept Cylinder Volume. The stock LS1 has a Bore of 3.900" and a stroke of 3.622" giving a Swept cylinder volume of 709.04cc

Adding up items 1-4 gives the Total Combustion Volume.
So, If I use the formula (Swept Cylinder Volume + Total Combustion Volume) / Total Combustion Volume = these results using a .060 MLS gasket:

72.27cc = 9.59 CR
71.71cc = 9.65 CR
71.05cc = 9.72 CR
70.59cc = 9.77 CR
70.03cc = 9.83 CR
69.74cc = 9.87 CR
68.91cc = 9.96 CR
68.35cc = 10.02 CR
67.79cc = 10.09 CR
67.23cc = 10.15 CR
66.67cc = 10.22 CR (stock LS1 head spec) ?
66.11cc = 10.29 CR
65.55cc = 10.36 CR
64.99cc = 10.42 CR
64.43cc = 10.50 CR (stock LS6 head spec)
63.87cc = 10.57 CR
63.31cc = 10.64 CR
62.75cc = 10.71 CR
62.19cc = 10.79 CR
61.63cc = 10.87 CR
61.07cc = 10.94 CR
60.51cc = 11.02 CR
59.95cc = 11.10 CR
59.39cc = 11.18 CR
58.83cc = 11.27 CR
58.27cc = 11.35 CR

using a .052 graphite gasket gives these results:
72.27cc = 9.76 CR
71.71cc = 9.82 CR
71.05cc = 9.90 CR
70.59cc = 9.95 CR
70.03cc = 10.01 CR
69.74cc = 10.04 CR
68.91cc = 10.14 CR
68.35cc = 10.21 CR
67.79cc = 10.27 CR
67.23cc = 10.34 CR
66.67cc = 10.41 CR (stock LS1 head spec) ?
66.11cc = 10.48 CR
65.55cc = 10.55 CR
64.99cc = 10.63 CR
64.43cc = 10.70 CR (stock LS6 head spec)
63.87cc = 10.78 CR
63.31cc = 10.85 CR
62.75cc = 10.93 CR
62.19cc = 11.01 CR
61.63cc = 11.09 CR
61.07cc = 11.17 CR
60.51cc = 11.25 CR
59.95cc = 11.33 CR
59.39cc = 11.42 CR
58.83cc = 11.51 CR
58.27cc = 11.59 CR

If the piston is shoved back into the head to +.005 Piston Down Bore that gives a deck volume of .98cc. If an MLS gasket is used with this parameter changed the results are as follows:

72.27cc = 9.34 CR
71.71cc = 9.39 CR
71.05cc = 9.46 CR
70.59cc = 9.50 CR
70.03cc = 9.56 CR
69.74cc = 9.59 CR
68.91cc = 9.68 CR
68.35cc = 9.74 CR
67.79cc = 9.80 CR
67.23cc = 9.86 CR
66.67cc = 9.92 CR (stock LS1 head spec)
66.11cc = 9.99 CR
65.55cc = 10.05 CR
64.99cc = 10.12 CR
64.43cc = 10.18 CR (stock LS6 head spec)
63.87cc = 10.25 CR
63.31cc = 10.32 CR
62.75cc = 10.39 CR
62.19cc = 10.46 CR
61.63cc = 10.53 CR
61.07cc = 10.60 CR
60.51cc = 10.67 CR
59.95cc = 10.75 CR
59.39cc = 10.82 CR
58.83cc = 10.90 CR
58.27cc = 10.98 CR

If the piston is shoved back into the head to +.005 Piston Down Bore that gives a deck volume of .98cc. If a graphite gasket is used with this parameter changed the results are as follows:

72.27cc = 9.49 CR
71.71cc = 9.55 CR
71.05cc = 9.62 CR
70.59cc = 9.67 CR
70.03cc = 9.73 CR
69.74cc = 9.76 CR
68.91cc = 9.85 CR
68.35cc = 9.91 CR
67.79cc = 9.98 CR
67.23cc = 10.04 CR
66.67cc = 10.10 CR (stock LS1 head spec)
66.11cc = 10.17 CR
65.55cc = 10.24 CR
64.99cc = 10.30 CR
64.43cc = 10.37 CR (stock LS6 head spec)
63.87cc = 10.44 CR
63.31cc = 10.51 CR
62.75cc = 10.59 CR
62.19cc = 10.66 CR
61.63cc = 10.73 CR
61.07cc = 10.81 CR
60.51cc = 10.89 CR
59.95cc = 10.96 CR
59.39cc = 11.04 CR
58.83cc = 11.12 CR
58.27cc = 11.20 CR

There are other factors that change CR but they are relatively minor compared to these variables. I am by no means discrediting the work done by Tin Indian or even contesting the published figures. I just took the tables and extrapolated them with different variables other than stock for cc volume and swept cylinder volume. What appears to me, if I am to justify GM's published CR specs for LS1 and LS6 engines are as follows. LS1 uses 66.67cc combustion chambers, .052 gasket thickness, and a Piston Down Bore @ TDC of +.005". An LS6 engine uses a combustion chamber of 64.43cc, .060 gasket thickness, and a Piston Down Bore @ TDC of -.008". Does this point to a design difference between the LS6 block and the LS1 block I am not aware of? It would be nice to know the spec for LS1 and LS6 deck volume. I personally have a 99 LS1 that is clearly and old-style LS1 block. Are my pistons sticking up out of the hole .008 or are the down the hole .005? This makes a huge difference is computed CR and it would be a great help to the guys changing heads and getting them shaved to know this.

 

Im about to have installed : west coast cyl heads casting #241 ls1 heads: ls1 stage 1+ ported. valve job 2.02/1.57 rev valves 5 angle cut. MILLED .030 chamber size 62cc compression ratio 10.8:1 or 10.9:1 new 918 springs ready to just bolt-on. The custom grind cam going in , is comp cam 228/228 .588/.588 114+2 Im worried about the p/v issues , but the installer and my ls1tuner has do this set-up to so many cars, and they say it will be fine, they are even running this set-up on one of my tuners cars. I thinking about ordering the cometic thicker head gaskets. Please advise on what i should do! Any advise on p/v issues will really help me quit worring! thanks jerry

 

You will be fine with that setup.. Will clear easily.

 

thanks bigeller

 

heres one for you guys, if using a 6.0L block with 10.1 C/R with the stock 317 heads, if you bolted on stock LS1 heads, the C/R would go up correct ? any body got a number ?? The 317 heads have a 73cc chamber , and the LS1 heads have a 66cc chamber, so it WOULD go up right ??

 

That is a great question and the same one I had relative to my former setup.. I have a 10.1 Escalade engine.. The stock #317 heads are 71.06cc. I had a set of #243 LS6 castings that were bare initially, and were approximately 70cc.. I had them milled .020" Which should be something similar to the 66.67cc stock LS1 heads on a 3.898 bore..

The only accurate way to measure in my car would be to have the chambers cc'ed .. I would guess I was around 10.4:1..since the heads had been ported..

To answer your question.. Yes your compression ratio will increase.. I would guess you'd be at around 10.6:1..

 

anybody else got an answer ?? I have been doing research, and need to see if the block I have is an LQ4 or LQ9......I asummed that the iron block with alum heads had 10.0 to 1 C/R. but I have since read that the diff between the two are the pistons, if they are flat top pistons, it is 10.1:1, if they are dished pistons, it is more like 9.5:1 if anybody knows chime in

 

Sorry, I thought you already knew which engine you had when you said it was 10.1.. The blocks are the same between an LQ4 and an LQ9.. The LQ9 has flat tops and the LQ4 has dished pistons.. Mine is an LQ9 10.1 engine..

If you have an LQ4, which is the lower compression engine, you'll wanna put some LS1 or 4.8/5.3 truck castings on it to up the compression for an NA setup.

Your last sentence is correct.

 

Up to what compression ratio can 93 octane handle well?

 

Damn u guys confused the hell out of me. So can someone help me with this question? I have a 98 block with stock internals. I want to put 6.0 heads on it because I have a set laying around. How can I get my compression ratio in the 10s? Can I get thicker head gaskets or do I have to get the heads shaved. Also I can get my hands on any rods, pistons, or crank from any new gen motor. Is there any they are the best to use?

 

thicker gaskets decrease compression. exactly what CR are you trying to get "10's" is a broad number. if you can get the 02+ ls6 rotating assembly.

 

I have a stock LS1 and I want to put 2001 and up 6.0 heads on it but I want my compression to be around 10.1. I was curious if 6.0 internals will work in an LS1?

 

milling the heads .030 will put you back at 10.1 w/ a stock gasket. and everything but the pistons (obviously) are interchangable.

 

So if I use a ls1 block I can put in 6.0 crank and rods and use LS1 or LS6 pistons Right? Do I have to get this line bored? and what would my cubs be?

 

your cubes will be stock; 3.90 bore x 3.622 stroke. and yes all internals sans pistons will fit. i'd say any machine work would be dependent on the condition of the block used.

 

 

if i have a dome shape piston with 1.299 piston height with 59cc LS6 heads that yeild to 13.1 CR.. is there a formula that i can calculate the Cr .. i need to lower the Cr by getting a new heads with higher CC to 11.5:1..

 

Quick question: with the pre-LS1 SM engines, if the heads were milled (for whatever reason) the intake manifold surface also had to be milled a smaller amount to align the bolt holes and eliminate the gap between block and the front/rear of manifold. Does the geometry of the LS1 heads require the milling of the intake manifold surface if the block mating surface is milled?

TIA...JJ

 

I am going to go for approx 10.7-8 CR on a std bore / stroke LS1 block with the std graphite gaskest. What I'd like to know is what is the best after marlet cam for the LS1 to put it power wish a little beyond a std LS6? I beleive there is a GM part no for a cam past LS6 spec that comes with a softer set of springs in the kit as well. Does this sound right - any idea's what this no. is and what kind of power over std I could expect from the CR raise and the above cam and spring (nothing else planned - no porting) - maybe using later LS6 intake maniford.
Cheer Jon