Opinions on DCR and SCR
Here are a couple static and dynamic compression work ups. One for an LS6 as a benchmark test to confirm that accuracy of all data. We know that with these ls6 specs, we should get 10.5:1 and we do. Then we only change the head volume and we get 11:1 static with an 8.5 dynamic. I have confidence in these numbers. So, this should be your actual numbers with your 60.5cc heads.
I don't want to confuse the issue anymore. I am using the specs for a stock head gasket. I also don't want to use "0" for the piston volume because that is just not correct. Even a perfect flat top piston has some volume because of the area above the rings. This is a nice way that the OP can see what his actual compression with the cylinder heads he wants to use.
I don't want to confuse the issue anymore. I am using the specs for a stock head gasket. I also don't want to use "0" for the piston volume because that is just not correct. Even a perfect flat top piston has some volume because of the area above the rings. This is a nice way that the OP can see what his actual compression with the cylinder heads he wants to use.
Hmmmm... I feel like you are confusing me though. I'm using the numbers posted in J-Rod's thread: https://ls1tech.com/forums/generatio...learances.html
Where are you getting 1.4 cc's for the piston? I have stock pistons with no valve relief. Are you estimating the volume in between the tapered section of the rings and bore? I've never seen anyone add that in.
Also, where did you get the head gasket bore to be 3.94? This is what I have: http://sdparts.com/details/gm-perfor...parts/12498544 I've always heard 3.910
Where are you getting 1.4 cc's for the piston? I have stock pistons with no valve relief. Are you estimating the volume in between the tapered section of the rings and bore? I've never seen anyone add that in.
Also, where did you get the head gasket bore to be 3.94? This is what I have: http://sdparts.com/details/gm-perfor...parts/12498544 I've always heard 3.910
Last edited by mamead; Mar 13, 2011 at 08:18 PM.
Hmmmm... I feel like you are confusing me though. I'm using the numbers posted in J-Rod's thread: https://ls1tech.com/forums/generatio...learances.html
Where are you getting 1.4 cc's for the piston? I have stock pistons with no valve relief. Are you estimating the volume in between the tapered section of the rings and bore? I've never seen anyone add that in.
Also, where did you get the head gasket bore to be 3.94? This is what I have: http://sdparts.com/details/gm-perfor...parts/12498544 I've always heard 3.900
Where are you getting 1.4 cc's for the piston? I have stock pistons with no valve relief. Are you estimating the volume in between the tapered section of the rings and bore? I've never seen anyone add that in.
Also, where did you get the head gasket bore to be 3.94? This is what I have: http://sdparts.com/details/gm-perfor...parts/12498544 I've always heard 3.900
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This is the compression calculator that I used:
http://www.kb-silvolite.com/calc.php?action=comp
As far as the head gasket bore goes, sorry, i guestimated.
However, if you take anything away from this, it is that you need to have a benchmark to check your numbers. Use the LS6 numbers because you know the compression ratio is 10.5:1. Once you have all your known numbers in the calculator for the LS6 with a head volume of 64.43 to come up with 10.5:1, then you can change the head volume only to 60.5 and you will know the correct numbers.
You would do best not to compare different compression ratio calculators because some calculators may attempt to figure in piston volume above the rings while others do not. The calculator link above does not try to figure that in. So, you will have to supply it. And, since you do not know that number, you will have to use the LS6 benchmark to work backwards and figure it out.
http://www.kb-silvolite.com/calc.php?action=comp
As far as the head gasket bore goes, sorry, i guestimated.
However, if you take anything away from this, it is that you need to have a benchmark to check your numbers. Use the LS6 numbers because you know the compression ratio is 10.5:1. Once you have all your known numbers in the calculator for the LS6 with a head volume of 64.43 to come up with 10.5:1, then you can change the head volume only to 60.5 and you will know the correct numbers.
You would do best not to compare different compression ratio calculators because some calculators may attempt to figure in piston volume above the rings while others do not. The calculator link above does not try to figure that in. So, you will have to supply it. And, since you do not know that number, you will have to use the LS6 benchmark to work backwards and figure it out.
I guess that makes sense. The only though is when I am reading what other people are running as SCR and DCR, I don't think they are taking those into account for their calculations. I understand what you mean though but if I am going to compare against others, I have to use the same method as theirs I guess. I'm going to run it and like someone mentioned before, full up on 91 when I go for my tune. I'll try to run 93 whenever possible but won't have to worry too much if the gas station only has 91. I'll post up my results after the tune.
Here is an article that talks about not forgetting the piston volume around the ring area:
http://www.chevyhiperformance.com/te...ide/index.html
Here is the excerpt that applies:
While they make the general statement that it probably not be more than 1cc. You may see it between 1 and 2cc on some pistons. Most guys probably aren't aware of the above unless they spent time in a machine shop.
http://www.chevyhiperformance.com/te...ide/index.html
Here is the excerpt that applies:
Speaking of accuracy, there is another small volume that is usually ignored but also contributes to compression. This is called the crevice volume and is the tiny volume between the compression ring and the top of the piston. Typically this will not increase total volume by more than 1 cc, but if you’re looking for complete accuracy, it should be included. The best way to account for crevice volume is to measure the entire piston/cylinder assembly with the engine assembled. Using a flat plastic plate with a hole drilled in the top, you can place the piston ½ inch down the cylinder and then fill that volume from a measured burette. Then compare the volume of a perfect cylinder to the amount you measured. The difference will be the combination of any piston top valve reliefs and the crevice volume.
My DCR is calculated at 8.606 and I run 93 all the time. It doesn't take a whole lot of spark timing though; 17-19 degrees in the 4600 RPM area. I can get nutty with some C12 though.
