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55 Chevy · 09-24-2008, 01:55 PM

Yes the old '56 265 991 castings can safely be bored .125 while the 57 265 548 castings can go even more.About .165 I think. 1958-62 283's also had thicker cylinder walls & can be bored to 4.000" when new. In 1963 until 1967 GM changed the 283 & the cylinder walls were thinner. I believe about.060 was about the most you could go with those ones. Those ones would definitely be lighter than the 265 blocks.

09-24-2008, 01:55 PM	#4
55 Chevy Member Join Date: Feb 2008 Location: Calgary,Alberta area Posts: 229 Likes: 23 Liked 20 Times in 15 Posts	Re: SBC cylinder wall thicknesses? Yes the old '56 265 991 castings can safely be bored .125 while the 57 265 548 castings can go even more.About .165 I think. 1958-62 283's also had thicker cylinder walls & can be bored to 4.000" when new. In 1963 until 1967 GM changed the 283 & the cylinder walls were thinner. I believe about.060 was about the most you could go with those ones. Those ones would definitely be lighter than the 265 blocks.