LS-6 block.
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From: Twin Cities, MN
LS-6 block. Just found out that the block we have isn't an LS1, it is an LS6. Other than the LS6 intake, I believe we have the rest of it as an LS1. Block read 12561168. Heads are 241 which I believe means LS1. Does this discovery mean anything? Does it matter? Are there any little gotcha's we need to watch for, and most importantly, what else would we need to finish making this an LS6?
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Joined: Dec 2004
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From: Baltimore, MD.
From what I understand, the difference between the LS1 and 6 blocks are fairly minimal. Basically, it boils down to the "windows" that are in the block for bay to bay breathing. The bulkheads between each pair of cylinders (1/2 & 3/4, 3/4 & 5/6, and 5/6 & 7/8) have windows to allow air to move around as the cylinders move around. The LS6 has better windows.
The rest of the differences are all up top, where it's important:
Cylinder heads with lighter valves (and really good ports).
Camshaft with extra lift / duration & reduced base circle.
Longer pushrods because of the reduced base circle.
Better springs to handle the extra lift.
LS6 Intake (obviously) is significantly better than the LS1 intake.
I think the LS6 block may have been used on the late f-bodies ('02's) when the LS6 intake was also used (as a running factory change). But without the rest of the parts (heads, cam, valves, pushrods, springs) it's really still an LS1 (cylinder heads & cam are the key to power).
'JustDreamin'
The rest of the differences are all up top, where it's important:
Cylinder heads with lighter valves (and really good ports).
Camshaft with extra lift / duration & reduced base circle.
Longer pushrods because of the reduced base circle.
Better springs to handle the extra lift.
LS6 Intake (obviously) is significantly better than the LS1 intake.
I think the LS6 block may have been used on the late f-bodies ('02's) when the LS6 intake was also used (as a running factory change). But without the rest of the parts (heads, cam, valves, pushrods, springs) it's really still an LS1 (cylinder heads & cam are the key to power).
'JustDreamin'
Originally Posted by 67rsss
Our casting number says it is. We were just wondering if it was anything to be worried about....
Joined: Sep 2004
Posts: 3,148
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From: Downers Grove, IL
Don`t be worried, be happy The LS6 block is better. The windows are larger which makes a difference high up in the RPMs, I forget what RPM it is exactly, but somewhere up past 6k or 7k the windows in the LS1 blocks do not flow enough air and problems start to develop. They made the windows larger in the LS6 block so that they could safely spin more RPM.
The LS6 block is better. The windows are larger which makes a difference high up in the RPMs, I forget what RPM it is exactly, but somewhere up past 6k or 7k the windows in the LS1 blocks do not flow enough air and problems start to develop. They made the windows larger in the LS6 block so that they could safely spin more RPM. 
