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I'm new to the forum so forgive me if this has been posted before. I recently purchased a 12561168 LS6 block, it was in a guys garage in a wood crate wrapped in plastic and he assumed it was a LS3, which it wasn't, the block is brand new never been used, never had a head on it, dowels never put in, never had a cam in it etc, the cylinder walls were horrible, rough as hell and I didn't have calipers with me so I paid the 100$ and took it home. Ran a dial bore through it and the dial read 3.840 in ALL cylinders, virgin liners, and a virgin deck that is .008 to tall. The liners Sonic check at . 212 and the rest checks out good. Why wasn't this bored from GM?
My guess is factory blemish, see how far you can hone it out, get every thing from summit racing, use a sensible cam, build it up, run the **** out of it, enjoy.
In the photos it looks to me like the No.1 cylinder has been re-sleeved. The other cylinders I can see look like they have been honed and it looks like cross-hatch in there.
The cross hatch was me with a scotch Brite to remove some surface rust to check diameter. I think I'll bore it and put this K1 3.900 stroke crank in it and run it. Cylinder 1 looks like the rest I just put a light in it to intensify the roughness of the cylinders, it does need decked but it'll make a good Street engine.
My guess is factory blemish, see how far you can hone it out, get every thing from summit racing, use a sensible cam, build it up, run the **** out of it, enjoy.
That sounds really reasonable to me. There were a lot of surplus and factory blemish LS6 block floating around back in 2002-2005. I have one.
I suggest checking to make sure the block has all of the bolt holes drilled and sensor holes. Once someone built and LS6 and found out as the motor went in the car the block didn't have the crank position sensor hole machined...
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Ls6? 
