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A stock LS3 has 10.7. Are you talking about shaving the heads? As far as LS engines in general, Ive heard of guys getting away with close to 12 to 1 WITH a spot on tune.
It's a balancing act with the LS3 heads. Too much CR and you can't crank in enough timing to make power. I ran 12:1 and could only run 24-25 degrees of lead. At 11:4, I ran 29 degrees and made more power. These heads LOVE timing.