Hello all,

I have hesitated to post this question as I have tried to find a functional search feature without success, so please forgive in advance.
My question is whether or not the B9AE-6015-F cylinder block can be safely overbored to a stock 312 bore size (3.800")?
I see a lot of references that say this block was used as a 312 base if it came with the ECZ main caps but since this engine came from a truck, it seems unlikely that I will have gotten that lucky.  I am not yet in a position to tear into it quite yet but am trying to get my head around a reasonable build plan ahead of the teardown and inspection.  Thanks in advance for any help and humoring a rookie!

Regards,

Sven Pruett

Sven Pruett
1970 Boss 302 Mustang - https://www.instagram.com/night_mission_customs/
1956 Thunderbird - 312 Y-Block

While the B9AE-F blocks were used for both the 292 and 312 engines, sonic testing of those blocks indicates that those engines were being cast differently to support the different bore sizes. The same holds true for the ECZ blocks that were used for both the 292 and 312 engines.  As a general rule, most Y engines are safe for an initial 0.060” overbore but as general rules go, there are going to be exceptions.  It’s always recommended to sonic test the cylinder wall thicknesses prior to boring to ensure that core shift is not going to be an issue.  Boring any 292 block 0.050" oversize to get a standard 312 bore is not expected to be a problem but sonic testing will always give some assurance that the block is going to a safe candidate for that.

Lorena, Texas (South of Waco)

The block in my 55 Tbird is a 1956 ECZ-A 292. Although the car has been in the family for 50+ years, I knew very little about it's history (my dad wasn't the original owner). When pulling one of the heads, I discovered that it had + .060 pistons. Not knowing what it would take to clean it up, I started searching for another block. I now have a standard-bore B9AE 292 block. The block was cleaned & magged, but not sonic tested. I intend to have it bored + .075 (3.825). I've already purchased the pistons and rings. 

I did a visual inspection and checked the spacing between cylinders, but I don't see any evidence of core shift. I plan to take the block to Tim McMaster for machining within the next month. If he recommends sonic testing the block, I will authorize it. I have too much money invested in parts to do otherwise. 

Thank you Ted!  That is exactly the response and detail I was hoping for!  

Sven Pruett
1970 Boss 302 Mustang - https://www.instagram.com/night_mission_customs/
1956 Thunderbird - 312 Y-Block

I am in a similar boat.  My 56 was a very poorly kept car when it was bought and put away in 1984.  The engine looks to be a straight pull from a '60-ish pickup and dropped in place of the long-gone 312 with only the intake and exhaust systems moving over from the original engine.  Ugh!

Sven Pruett
1970 Boss 302 Mustang - https://www.instagram.com/night_mission_customs/
1956 Thunderbird - 312 Y-Block

Everything from the heads up, excluding the 57 distributor, were/are all original 55 Tbird, which makes me wonder why the original 55 short block was replaced with a + .060 56 ECZ-A. I don't know if the original owner replaced it or my dad (2nd owner), but neither is still around to ask,