Hot Rods Question regarding a Ford FE engine.

I have a question that, after much searching, I still have not been able to find the answer. I have a C5AE 390 block that came from a 335 hp Comet. The question is, that on the back of the block, behind where the flywheel would be, the casting has 427 cast right onto the block. Was this engine cast as a 427 block, and because of demand bored as a 390?
I have pulled the casting plugs, and the measurement leads me to believe that there is enough meat to bore it out to 427 ci.
Does anyone know the story of these blocks?
Bob

 

look on the fe forums , jay brown's is a good one , lots of imfo , probably not a 427 .

 

Maybe someone can back me up on this as I'm not 100% sure that this is true, but I'm pretty sure it's just a casting mark, like the 352 stamped into the front of all fe blocks.

 

I think you are probably right......

LynnW

 

From what I understand, Ford had different molds for casting cylinder blocks and at times the rear mold for a 427 was used on a plain 390 block. But some blocks did have thicker cylinder walls than others, again from using different molds when pouring blocks. The only way to be sure is to "sonic" check the wall thickness. There has been 390 blocks that have enough "meat" to bore to 428 bore, an overbore of .080 to 4.130. Whether it could go the 427 bore of 4.230 is something else..

 

http://www.mre-books.com/interchange/interchange11.html

 

I have seen a lot of FE blocks, but this is the only block I have seen with that particular casting mark. I have checked the thickness of the cores by measuring the distance between the outer of the cylinder bores, and it would easily bore out to 4.25 with .125 wall thickness.
I'll leave it as a 390, but it is nice to have the answer to something I have been curious about since I bought this engine.
Thanks for the info.

 

Trying to determine what you have from casting numbers is an exercise in futility on a FE. The 427s are about the only ones that can be identified visually due to the cross-bolts, and on the side oilers, the visible 'ridge' down the side of the block. As far as overboring them, none of the smaller FEs has been successfully punched to the 427 bore size that I'm aware of; there's simply not enough meat there. You can punch some 360/390 blocks out to the 428 bore, but sonic checking is always recommended. Some builders favor the truck blocks for this. Some early (58-61) 352 blocks can take the 428 bore, but by '62 Ford was using thinwall casting across the line and the later 352 blocks wouldn't go out that far.

 

Fe's are weird when it comes to what the casting numbers mean, mine has a big "59" cast into the crankcase and so far i haven't found what that is, guess its just a random number.
if it doesn't have the triple main bearing web, i'd assume its nothing more than a standard 390.

 

If you have the center frost plugs out, do the old drill bit test. Of course this doesn't account for core shift, corrosion, wear, etc but it should get you close to understanding exactly how thick the cylinders are. It would not be unheard of, but pretty unlikely that Ford would machine a raw 427 casting to 390 specs.

.375"
3/8"
No Good

.312"
5/16"
No Good

.281"
9/32"
4.080" Max

.218"
7/32"
4.160" Max

.187"
3/16"
4.18" Max (In a 406 or 428, Good Block)

.187"
3/16" (427)
4.293" (68 C8AZ-6010-G) .125''

.125"
1/8" (427)
4.310" (Marine Block & Some Early 427's)

 

The numbers that seem cryptic cast in FE blocks only mean something to the guy who works in the foundry. There are several molds used to cast a block and what you are seeing has to do with which piece of the mold it is. I am not absolutely sure but I think that I have read somewhere that the blocks were not all cast in the same foundry which would also explain the different numbers on the blocks that don't seem to mean anything.

I have found that it is easier to not get caught up on numbers and casting marks and just build what you know that you have.

 

I want to assure you, that I don't wish to waste a desirable block on a gamble. What bothered me, is that I had read articles published in what I would have considered reliable publications that stated if the distance between the cores passed the drill bit test, that it was a suitable candidate for a bore. After further reading, I found the answer. This HAMB thread below, that didn't come up on my first search, says it all.
It just drove me nuts, knowing that I had a possible candidate for a 427. I have a 428 CJ engine that I will use instead. Thanks for all the input.
390 FE service block 427 bore?
https://www.jalopyjournal.com/forum/threads/390-fe-service-block-427-bore.639277/