Maximum Recommended 312 Bore


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By 55blacktie - 3 Years Ago
What is the maximum bore recommended for a 312? John Mummert's "Dimensions" Table shows up to .060. If the 312 blocks start out as 292s, you're talking about + .110 bore increase. I know the early blocks are supposed to have thicker cylinder walls (maybe for that reason).
By DryLakesRacer - 3 Years Ago
Some where in one of my Ford manual or books their RECOMMENDED maximum bore for a 292 was +.040”. We know +.060” pistons and rings are available. 
A +.050” 292 is a stock bore on a 312”. With that knowledge a +.040” over 312. Is a+.090” 292. I would sonic any  block I wanted to use either 292 or 312. 
For me if I wanted a 312 and had the crankshaft and rods, I would find a good 292 block and bore it +.050” and have the crankshaft mains ground to 292 main specs. Std 312 pistons and rings are available along with rod and mains for a 292. 
By Ted - 3 Years Ago
The 312 blocks had their own block castings until the C2AE blocks came out.  With the introduction of the C2AE blocks, those blocks became shared for both the 292 and 312 requirements.  While 312 engines were no longer available in vehicles, the 312 engines and blocks were still being produced for service replacements, industrial, and marine usage.  The C2AE blocks were cast for both 292 and 312 usage at least to the end of 1967.

As a general rule, the cylinder wall thickness for pre ’62 blocks for both the 292 and 312 blocks is suitable for a 0.060” overbore.  Each block had its own bore limitations so don't be taking the 292 blocks out to the extreme before testing for cylinder wall thickness.  For normal applications, that would make it 3.810” bore for the 292 blocks and 3.860” bore for the 312 blocks.  Core shift issues do make for some problems though if attempting to go larger than this and trying to make some serious power numbers.  Low compression engines are obviously more tolerant of larger overbore (thinner cylinder walls) than those engines built with higher compression ratios.  The performance level is always a consideration when boring those engines beyond the normal limits.

Sonic testing of the 292 blocks does allow for those ‘better’ blocks to be picked out thus allowing for up to 0.110” overbore which would effectively be a 0.060” over 312 size.  Another option for standard bore blocks is to determine exactly where the core shift in the cylinders resides and then offset bore accordingly to equalize the cylinder wall thickness.  The 603HP EMC engine was a 292 block with 0.110” overbore but that block was hand picked for its cylinder wall integrity and having reinforced mains.  Sonic testing is your best friend when taking the cylinder wall bores out to the extreme.
By 55blacktie - 3 Years Ago
On ford-y-block.com, Block Numbers," John Mummert said that 292 and 312 blocks were of the same casting, with the same numbers. if that's true, how can both be bored .060 over, when the 312 is already .050 over?
By 55blacktie - 3 Years Ago
Did Ford continue casting 312 blocks after 1960, the last year in which the 312 was available in some Mercury models? I wasn't aware that there were any C2 312 blocks.
By darrell - 3 Years Ago
they found one C2AE block used as a marine engine.ford sometimes run of a batch of replacement blocks.they did that with the 272 in 59 B5AE.
By Ted - 3 Years Ago
FoMoCo continued casting the C2AE blocks at least thru the end of 1967.  The C2AE blocks were used for both the 292 and 312 block requirements while the 292 blocks continued to use the EBU main caps and the 312 blocks used the ECZ caps.

As a general rule, the EDB blocks are 292 and the ECZ blocks are 312.  I have seen a limited number of ECZ-C blocks used for the 292 blocks but those had the EBU caps and cylinder walls adequate for a +060 over 292.  Those same ECZ-C blocks cast for 292 usage when sonic tested would not make suitable +060 over 312 bores.  To date I have not come across any ECZ-A or ECZ-B blocks used for the 292 engines.  All ECZ-A and ECZ-B blocks have been 312’s thus far.  Likewise, I have seen one instance where a EDB block was used for a 312 but all other instances have been 292 engines.

The best identifier for which engines the blocks are cast for are the main caps:  EBU caps for the 292 blocks and ECZ caps for the 312 blocks.  When in doubt about the cylinder wall thickness, just have a sonic test of the cylinder wall thickness performed.  Some of those late 1954 ECG 272 blocks will surprise you.