SBC cylinder wall thicknesses?
 

Anybody got an idea what the older SB Chevy blocks (cast prior to 1962) measure up in a sonic test? How does that compare to the best 350 blocks? I think I read that Chevrolet changed or tried to make lighter at least 3 or 4 times over the years.....I think the mid/late '80's were the start of the worst when they started to crack in the valley area....I know a bunch of the early stuff (especially the 265) could be bored out to even .125" SAFELY....but you sure couldn't do that with today's production stuff! I once lifted a 265 bare block and it felt a ton heavier that the 1964-283 we are running....Not talking about GM Performance stuff here....which I'm sure have the 'beef' in all the right places!

Re: SBC cylinder wall thicknesses?
 

I have been told that you need at least .175 wall thickness on the thrust side. The bowtie block is the way to go. The old 4 bolt 350 blocks with the long ID pad are usually OK at .060 over.

Re: SBC cylinder wall thicknesses?
 

Do the smart thing and map each cylinder by sonic checking.

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.

Re: SBC cylinder wall thicknesses?
 

How about original Chevy II blocks, both 283 and 327? How do these fair in strength and cylinder wall thickness? I have been told that in years past before the introduction of the bowtie blocks, these were sought-after by racers.

Re: SBC cylinder wall thicknesses?
 

The small journal 327 blocks were proned to splitting cylinders if you ran them at 060 over. You would be better off with a 4 bolt large journal block. I am not sure about the 283 stuff. I have a real early 1962 small journal block in my car now and it seems to be a good one. They are real hard to come by. Sonic checking was real popular before the bowtie blocks. It was a waste to do all of the machine and prep work on a production block then have it split a cylinder after 10 - 15 runs.

Re: SBC cylinder wall thicknesses?
 

Why don't you guys just sheeve the cylinders? It's $80 a cyl & a hell of a lot stronger.

Re: SBC cylinder wall thicknesses?
 

Who will do it that cheap and does that include the sleves and what material is it??
Also beware on stock SBC blocks the sleves get dangerously close to the bolt holes and almost always crack to those bolt holes... Bowtie Blocks are no problem and will work well for sleeved down for say 305 \ 283 \ 265 ...

Re: SBC cylinder wall thicknesses?
 

Bub, I sent you PM, Tom

Re: SBC cylinder wall thicknesses?
 

Thanks guys.....what about thickness of finished bores in the early 265/283 blocks? Any ideas on this and how it compares to best 350 situation? Isn't there a small-bore Bowtie block available with an unfinished bore size of about 3.7" so you can bore/hone to the desired size instead of sleeving down for the smaller displacement racers? Bub, is that sleeve/cracking problem more common in the larger or smaller bore production blocks or ALL of them? Thanks again!