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As I've mentioned in a couple other posts, I'm in the research phase of building a 421ci LS Series. There are several ways to get there, the attached Excel spreadsheet shows 3 ways to get there. My question is, has anyone ever bored a 6.0 out to 4.095? I'd love to go that route, but I don't think it is feasable. If I were to have a block sonic tested, how much material is recommended to be left around the bore after boring? This is going to be a N/A motor. Are there any blocks that are known to have thicker cylinder walls than others, LQ4 vs LQ9 vs L96 for example? I know there are other CI's that I could shoot for, and are safer builds, but I am going to build a 421 for it. It's going to go into an '81-'87 G-Body Grand Prix. 421 was the original large displacement motor in the early Gran Prix's and that is what I want to build for nostalgic reasons. I'm going to put the '66 421 badges on it also. I'm probably going to end up with the 4.04" bore and 4.1" stroke. I'd feel better with the 4" stroke, for bore side loading reasons, but if I can't get there with a Vortec 6000 block, then I'll probably go with the 4.04/4.1 build. I'll probably try to find an L96 to get the 823 heads.
4.065 is commonly done to iron 6.0’s, but I can’t see .095” happening without a resleeve.
talk to Erik at hpr, he does a lot of the big stroke engines. He specs a different piston than what’s available off the shelf to get them to wear less.
Stick with the 4 inch stroke or less. The cylinder sleeve gets to be an issue above 4 inches. Even some of the early LS motors the 4 inch stroke is getting much. Work with an engine builder that has done a few of these and can get it dialed in.
4.065 is commonly done to iron 6.0’s, but I can’t see .095” happening without a resleeve.
talk to Erik at hpr, he does a lot of the big stroke engines. He specs a different piston than what’s available off the shelf to get them to wear less.
Thanks, that's what I was thinking, just thought I'd ask if anyone had done or heard of it being done.
I’ve seen iron 6 liter blocks bored to 4.100 for N/A builds. I can’t comment on how reliable it is, but it’s been done quite a few times. Obviously it will depend on how the block sonic tests for wall thickness. I’m referring to gen4 blocks here.
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Vortec 6000 Overbore 
