Boring 390's

[Gregg]

Common sense answers throughout this thread.  Sometimes people just want to believe what they want.  I can't really imagine a sales campaign of "Look at our new thin wall engine block technology".  Folks may have cared about brand, most cared about price and options, some fuel mileage, some power.  In fact, some may have been put off by the "new fangled" thin wall technology.

[shady]

I rebuilt a mid '70s truck 390 in the early 80s that needed a bore. TRW made 60 over pistons so I figured what the heck, may as well go for the gusto. 500 miles later it hydro-locked. Pulling the heads I saw a split in one of the cyl. walls. I opened the split with a pry bar and couldn't believe how paper thin the wall was. After that, there was no going beyond .030 for me.

[GerryP]

Anyone -who is not me- care to explain exactly what "thin wall" casting is as far as engine blocks is concerned?

Seriously, if cubic inches are your primary concern, you should be building a Lima motor.  Very easy to get over 600 C.I. without even breaking a sweat or your budget.

[Gregg]

From Wikipedia (not the best source, but something)

The FE's thinwall casting production method was innovative and forward-looking in the mid-1950, resulting in lower weight and dramatically reduced production costs. Ford's competitors at the time required thicker castings to mask the flaws and defects that resulted from their processes. Improving quality and allowing thinner walls was accomplished through many engineering improvements, including reducing the number of cores required to cast an engine block. Fewer cores made it easier to assemble the overall mold for casting and reduced the number of potential problems. In the late 1980s when both Ford and GM revamped their V8 offerings, many of the FE's designs and engineering were incorporated in the new engines, including the deep skirt, cross-bolting of the mains and thinwall casting.

[GerryP]

From Wikipedia (not the best source, but something)

In this case, Wiki got it right, Gregg.  But to clarify, the "thin wall" isn't referring to just the cylinder walls, but to all the walls in the block.  This is pan rails, cooling jacket, cylinder walls and everything in the block.

[falcongeorge]

  Grab a block, sonic test it, and found out whether or not *that* block is thin because every block is a craps shoot. 

I'll be the first one to say that thick blocks do exist, because I had a '63 390 block that went that far without issue.  However, I wasted 2 to get to that point, and in hind sight, I accomplished ABSOLUTELY NOTHING by taking the one block out to a 4.130" bore.  Going from a 4.08-4.09 bore to a 4.130 bore doesn't open up magical gateways to head flow!  It does nothing but endanger the block's strength by making the cylinders weaker and it opens the block up to really weak spots due to pitting on the back sides of the cylinders that you can't see. 

If you do have a block that could go 4.130" and have plenty of meat left over, think about how rigid the block would be if you didn't do more than a clean-up cut.

hahaha, Brent knows something the rest of you guys don't. He aint gonna say it right out, and that suits me just fine, I aint talking anymore either. Someone once said that "George does not suffer fools kindly". Guilty as charged.

[blykins]

  Grab a block, sonic test it, and found out whether or not *that* block is thin because every block is a craps shoot. 

I'll be the first one to say that thick blocks do exist, because I had a '63 390 block that went that far without issue.  However, I wasted 2 to get to that point, and in hind sight, I accomplished ABSOLUTELY NOTHING by taking the one block out to a 4.130" bore.  Going from a 4.08-4.09 bore to a 4.130 bore doesn't open up magical gateways to head flow!  It does nothing but endanger the block's strength by making the cylinders weaker and it opens the block up to really weak spots due to pitting on the back sides of the cylinders that you can't see. 

If you do have a block that could go 4.130" and have plenty of meat left over, think about how rigid the block would be if you  didn't do more than a clean-up cut.

hahaha, Brent knows something the rest of you guys don't. He aint gonna say it right out, and that suits me just fine, I aint talking anymore either. Someone once said that "George does not suffer fools kindly". Guilty as charged.

Explain to me what I’m not going to say because I’m interested in hearing it.

[C6AE]

I built an A scratch 428 that took .060 just fine, but I wouldn't bet on another.

[WConley]

It's also notable that another old-school authority, Carl Holbrook, went to all of the trouble of sleeving and furnace brazing all eight cylinders on brand new CJ blocks for some of his race engines!  Having dead-nuts uniform cylinder walls was important to him for optimal ring seal.

If a guy as knowledgeable as Carl would go to all of that trouble, there's something to be said for keeping those walls as thick as possible.  As other smart guys here have said, the modern stroker kits and good heads are where it's at.

- Bill

[Drew Pojedinec]

I think most 390's are boring.

There, I said it.

[jayb]

LOL!  Well, I was thinking it....

[falcongeorge]

This conversation has continued on off-forum and some snickering has ensued. Apparently another FE Power member within about 20 miles of the "Area 51 Garage" had one of these "nonexistent" blocks ,and he mentioned to me that theres a third one (all three are early-mid seventies service blocks),  within 5 miles of my place. Im gonna try to find out if I can get a look at it, and hopefully stick a drill bit between the cores. But don't worry, we'll keep the results to ourselves, I don't wanna cause anymore emotional trauma.
Geez, three "non-existant" blocks in a 20 mile radius! Whoda thunk??!! Must be a disturbance in the gravitational field or something! Don't mind me, carry on with "all 390's are thinwall castings" internet groupthink, some of us are enjoying this...

[My427stang]

A drill bit test isn't going to prove much, the question is condition of cylinders and core shift.  The 2 bolt motor mount blocks seem a little more consistent, but after that, they are all over the map.  Last fall I turned down a 428 standard bore  irrigation motor for the hyd roller build in the dyno section because four on one back were "over and up" and I didn't trust the block at .030 and 500 hp. 

Of course if no-one checks, any block might work!

[plovett]

Well, thick and thin are subjective terms.  That's why I put thin in quotes.  There are some engines that can be bored 0.125" over and still have good cylinder wall thickness.  I would consider them "thick".  I think all FE's are "thin".  Sure, there is a lot of variation, but none are what I would call "thick".   It is not a criticism.  It is just a design feature of the block. 

JMO,

paulie

[plovett]

Let me clarify.    I don't think any factory FE blocks are "thick".  Aftermarket blocks are a different story.

JMO,

paulie