Do all Ford Y-Blocks from the 239 thru the 312 have the same (designed) cylinder wall thickness? 

292/312 blocks especially southern us the back 2 cylinders  subject to erosion due to no antifreeze. the last 2 292s I did (now retired) I had sleeves put in number 4 and 8
 in both cases water  had eroded them. due to the water flow one should learn wher  engine was used. northern  ones  not as vulnerable,as any freeze  limits erosion.

If I understand correctly, they have their own cylinder walls, not a common cylinder.  If they did, you could bore any of them to the 312 size or overbore.   Most will bore +.060" from their respective cubic inch new.  With sonic test some will go more safely.  Joe-JDC

JDC

Ted Eaton has used blocks that were bored +.110, but for racing only. A =.060 312 bore = 292 + .110. +.060 312 pistons are readily available, and 312 pistons can be used in a 292. However, the longer skirts of 292 OEM pistons will not clear 312 connecting rods, due to the longer 312 stroke. If 312 pistons are used in a 292, the longer 292 rods must be used with the stock stroke 292 crankshaft. 

My 1956 ECZ-A 292 block has + .060 pistons. When I rebuild it, I hope to use 3.825 312 forged pistons, but I will have the block sonic-checked for cylinder-wall thickness and core shift before purchasing pistons. 

The thick cylinder walled blocks are rare.  The ones I do find that will bore out the heaviest or to the extreme are some of the 272’s that were cast in 1954.  Beyond that, most Y’s safely bore +060 over their stock sizes.  Careful selection of blocks and offset boring where core shift is an issue will allow some additional overbore.

Core shift is always something to watch for and sonic testing will determine exactly where and how much core shift is prevalent within a particular block.  I have pages of sonic test date here and there does not seem to be a particular block casting after 1955 that gives a guarantee of going extreme on the bore sizing.  As has been pointed out, sonic testing will allow some blocks to be selectively bored out as much as 0.110” and still be thick enough for extreme performance use when normally aspirated.

If just wanting to arbitrarily pick a block, then choose a C1AE or C2AE block for the reinforced main webbing that came standard in those particular blocks.  The C2AE blocks were cast at least up to the end of 1967 so there are plenty of those still floating loose.

Lorena, Texas (South of Waco)

Thank you Ted and all others that responded. What I was really trying to ask was if the designed interior mold casting dimensions of all 239-312 blocks were the same; sounds like that answer is no, with cylinder walls (and various other interior dimensions) varying based on displacement.

Regards to All!

While it’s a common practice to bore the 272 blocks 0.125” over to make those blocks a standard bore 292, the cylinder walls in those blocks after doing so are on the thin side.  Here’s the sonic test sheet from one of those 272 blocks that was bored out to the 292 STD size. 
  

Lorena, Texas (South of Waco)

Is anything under 120 marginal?

Yes, especially on the Major Thrust side.  You can help stiffen a thinner cylinder wall by doing a partial block fill of the water jacket in performance applications.  Ring tension, piston to cylinder wall clearance, and rod ratio, stroke, rpm, compression are factors in just how much is a safe margin.  The non thrust sides are less of an issue, and many engines live just fine at or below .090" on the sides of the cylinder wall.  This is where a sonic test can make the difference in using a block or ruining one.  A good machinist can offset bore to take advantage of a thicker side of the cylinder core.  Joe-JDC  

JDC

20+ years ago when we rebuilt my 239 EBU I didn’t know anything. I just assumed one could turn a 239 into a 256. I guess we were just lucky. In 2017 we put a 312 crank in the 239. I cut the 272 standard bore piston skirts on our Shopsmith so they wouldn’t hit the crank throws. We ended up with a 283” 239. Would I do it again? No.

  Dennis in Lititz PA