Boring 390's

[67xr7cat]

I've been hearing the same stories all my life... this block is a thick wall casting, this block is high nickel, this block is a special high performance only came in GT40's and dump trucks....

I've seen a lot of sonic sheets for FE's and 385 series over the years and they go all over the map.  Rare is the block that can go .080" in all eight holes without thin spots, rare is the block that is too thin to go .030" too. What you have to realize is these are castings cast in the 1,000's of units. If you look back at what Ford was doing the move towards "thin wall" casting started in the early 50's.  Everyone thinks was all about using less cast iron, which of course was a goal, but you have to look at what was going on with the engine designs. The bore spacing was getting smaller and the bores getting bigger ( (relative to each other) leaving less room for the core. Thinner cores break easier and result in more scrap. If you can thin downs the walls you can maintain the needed core thickness. If you read some of the old SAE papers the industry as a whole was looking to build more compact engines, use less cast iron, and at the same time reduce scrap. When you cast blocks you always have blocks that get scrapped and blocks that have to be repaired. This is a huge deal and lowing that number was way more important than saving a few pounds in the casting process.

Bottom line in any block cast as a 390 meaning with 390 cores some will be thicker than other, but most will fall in the middle of the range. Is about what I've seen over the years and makes sense from a manufacturing point, especially when you take into account what was going on by the early 50's.

If you find a block with 428 cores that is a 390 then it is a 428, just like a 406 is a 406, and a 427 has a 427 core (which can vary by years...). If you have a 352 or 390 cast with the stand core and think can be bored out to a 427 by all means do. your block, your money, your time.  If it fails on your, well it is your wasted time, and wasted money. If it don't guess you got lucky. Is called gambling.

My suggestion is if you want a 428 block you need to find a block that has 428 cores meaning a 428 block, if you want a 427 you find a 427. Finally keep in mind all this stuff is 40 - 60 years old and just finding a good core that don't leak or have a crack can be hard enough.

[My427stang]

Agree with Brent 100%, periodically I find a decent 390, but I also had 2 that were real thin at .030.  I can't imagine a .125 cut, unless you find a real good block.

Make the bore straight, spend the dough on heads, intake and headers, if you want more displacement, add stroke

Falcongeorge, you get so wound up you miss what people say.  I have had 2 motor mount bolt blocks that can handle boring, not too many 4 bolt motor mount later versions, but take a breath, build whatever you want the way you want it.  Of course there are some, nobody debated that for a bit,

You don't have to agree with me, but I don't have to agree with you either.  Of course I have seen some thick ones, but your drill bit test doesn't guarantee it, no matter how much you get fired up, these blocks were not built precise, side to side they aren't even the same, even if the drill bit test checks good. 

Don't check 'em, check 'em, I don't care what you do, but once you get playing with a sonic tester, you'll be trying to figure out "how thin is too thin?" on the majority of 390s and industrial 428s, because that's what you will find. 

[plovett]

I know all of you are tired of this debate...….. But I want to clarify one thing.  Even if you find a 390 that can be bored 0.080" over and still have acceptable cylinder wall thickness for the intended use, it is still a thin wall casting, in my opinion.

It is just slightly less "thin".   

It is kind of like arguing philosophy.  It almost always eventually degrades into an argument about definitions.  What is "thin" and what is "thick"?

JMO,

paulie

[FERoadster]

I've been holding back this comment for days,  but did the "Ideal FE blue Prints" call for a block with thickness to be bored to 4.13 ??
Then manufacturing/casting tolerances would have been OK if there was no casting shift in the ideal world. Remember life will kick you in the A$$ and things get off kilter.
So in the perfect world with no casting shift could the as designed FE 390 blocks be bored to 4.13? Pre or post 1965? the date of 2 to 4 bolt motor mount pattern.
Inquiring minds.

Richard >>> FERoadster

[67xr7cat]

I know some on the other forum have some of the factory drawings so if they see this thread maybe they will chime in. I doubt Ford cared if a block could be over bored more than .030" which is the typical overbore for a rebuild, JMO.  Really, Ford is a manufacture casting blocks, making cars, trying to make a profit. If it made it out the door and out of warranty I doubt the foundry cared about if someone 30 years later can bore it .080" over.

My question has always been what is a safe wall thinkness? I'd say this number varies by use and everyone I ever asked had a different opinion on it. I can say you get under .080" on a non thrust and not likely to survive. .100" seems ok, .120" better... 

[jayb]

Hopefully all the enmity has gone out of this discussion, I'd hate to lock the thread because it has been an interesting topic.  For what it's worth, my personal limits for wall thickness are 0.125" minimum on major and minor thrust surfaces, and 0.100" on front and back.  The further down the bore the thin spots are, the more comfortable I am with the block.  And 427 blocks are different because the cross section of the bore looks like a cloverleaf, rather than a round cylinder.  My opinion is that on a non-thrust surface, you can go even thinner on a 427 block than 0.100", and in fact the 492" dyno mule I tested in my book was 0.060" over 427 block with the thinnest spot around 0.080".  That engine handled some pretty abusive dyno testing, up to 675 HP and 7000 RPM with 20+ different intake manifolds, and has never given up. 

And let's not forget the tune.  If you are on the edge of detonation you are much more likely to hurt the block than if you are running safe with good fuel and timing.  I personally think a manual trans is harder on a block than an automatic, especially on a car with slicks that's dumping the clutch at high engine speeds.  Higher horsepower will also stress a block more, obviously, with greater cylinder pressures.  Lots of factors at play here...

[FERoadster]

Yes I've got Shoe's prints but they are copies of the 427 only prints and involve 30 or so different sections to see an entire block.
I'm sending them to Lance Hargis (428Kidd) as a moderator on the FEForum since I only got them for safekeeping since I've got lots of space in my Library for things like that.

Richard

[winr1]

I had a D3 service block that the space between the cylinders looked tiny

It weighed 5 or so more pounds than my other 15 or so 390 blocks weighed
.........

Had 5 other 390 and 391 blocks that were heavier than my 352 blocks

Seems with larger bore would weigh less ??



Ricky.