Boring 390's

[frnkeore]

I'm a old mechanic, hot rodder/street racer and later a formula car, road racer.

Back in the 60's, it was common practice, to bore all engines 1/8", with the exception of the SBF. I know that Ford started using it's thin wall casting technique on the FE at some point. What was the year that that started? 

I've started looking for a 390 block for my base and would like to find one of the earlier ones as, I would like to do a 4.125 or 4.13 bore but, I'm not going to use Ford rods so, 428 pistons won't be a option.

If I can't find a early block, how large can you bore the thin wall 390?

 

[plovett]

Bore as little as possible.  Some 390's can go 0.060", but that is not a good idea in general.  I had one bored .080" over and it split a cylinder wall.  An 1/8" or 0.125" overbore is not doable on a 390.

JMO,

paulie

[Sand hauler]

Usually .040, but always do a Sonic check for core shift first to make sure. Unless you go with an aftermarket block BBM, Pond, Shelby, ECT . I believe that BBM also has 428 blocks also, just have to email them about it. The aftermarket block will go much larger.

[Yellow Truck]

I'm a old mechanic, hot rodder/street racer and later a formula car, road racer.

Back in the 60's, it was common practice, to bore all engines 1/8", with the exception of the SBF. I know that Ford started using it's thin wall casting technique on the FE at some point. What was the year that that started? 

I've started looking for a 390 block for my base and would like to find one of the earlier ones as, I would like to do a 4.125 or 4.13 bore but, I'm not going to use Ford rods so, 428 pistons won't be a option.

If I can't find a early block, how large can you bore the thin wall 390?

Pretty sure they were thin wall from the start. The 406, 427 and 428 blocks were specially (meaning more carefully) cast to avoid movement of the casting within the block. The issue with the 390 blocks was that they were done as cheaply as possible, which meant tolerating some casting movement, and having a slightly thin side in a production engine was not going to be a problem at a 4.05 inch bore. The 406 and 428s were 4.13 and the 427 was 4.2328 bores. You can't get there with most 390s, and you can't really over bore a 427 since the spacing is only 4.63 inches.

[frnkeore]

Paul,
With all due respect, I would have to have references for saying that early FE's were thin wall castings and that the 4.63 bore spacing, is the reason. The first report of thin wall castings, for Ford was for the '60 Ford Falcon (144/170) and in '62 for the SBF.

BTW, the 4.63 bore spacing, came from the 317/368 Linc/Merc, Y block engine (3.8- 4.0 bore). Another under appreciated short lived Ford engine. But won the PanAm race for Ford.

The 221 through 302 SBF, has a 4.38 bore spacing and they had 4" bores by '64. Even the '63, 427 had more room, between bores than the 289. I never heard of thin wall FE castings until much later than '63. I was born a Ford lover and racer (my dad worked for a Authorized Ford Rebuilder, shortly after I was born, in '44). I read everything regarding Ford, from the time I was at least 15 ('59), on. If it was in Hot Rod Magazine (and it would have been) I would have read it or in the Ford "Shop Tips" that was available from Ford Dealers when I was a mechanic.

Here is a small part of a article by Ak Miller and Lee Kelly, from 1971, where he suggested boring the 390 to 4.13 to clear 427 valves and calling it common. Not many people knew Fords better than Ak Miller.

[blykins]

I wouldn't recommend doing anything like they did it in the 60's....LOL

If you bored ANY Ford block an 1/8", you'd end up with a mess in the cylinders.   A 390 starts as a 4.050" bore, taking another .125" out would put you at 4.175".  Extremely thin.  A 428 starts as a 4.130" bore.  Taking another .125" out would get you to 4.255".  Thin.  A 427 starts at 4.230".  Taking .125" out would make a mess. 

Even on a 429/460, which starts at a 4.360" bore, taking .125" out would put you at 4.485", which isn't advisable.  Typically, .080" over is about all she wrote on those. 

So what do you think you'd gain by going to a 428 bore with a 390?  You gain 15 cubic inches and thinner cylinders.  Yes, you may gain a little help from an unshrouded intake valve, but I'd rather have a more stable and solid cylinder wall.   

With the new cylinder head and camshaft technology that we have today, there's 100's of ways to make big horsepower without compromising a good block. 

When I do a new build, I will generally try to open the cylinders up the least amount that I can.  With full custom pistons available, if I can get a round/straight bore at .005" over, then that's the way I go. 

[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]

there are a few 390 blocks around that will go +.080 and still be thick enough, but they are not common, and to go out and hunt one down is probably an exercise in masochism, if not futility.you willneed to sonic test any potential candidates, and if they are pitted on the water jacket side, you can still be in trouble. Brent alluded to the primary reason to do this, unshrouding a 2.19 intake valve. Its always about the cylinder heads.
 I wouldn't even consider trying to take any OEM FE block to +.125.

[blykins]

….and if they are pitted on the water jacket side....

That's the heavy hitter right there.  You can't sonic every single portion of a cylinder. 

[falcongeorge]

….and if they are pitted on the water jacket side....

That's the heavy hitter right there.  You can't sonic every single portion of a cylinder.

Its an issue. Depends somewhat on how thick the sonic test shows, and which way the core is shifted too.

[Yellow Truck]

Frank, I don't claim any special information. Having said that, I have never read anywhere that early FEs were not thin wall. I have read that Ford's reason for the FE architecture was the thin wall casting to create a lighter block. My mention of 4.63 spacing is that it tends to limit production bore sizes, and later over bores, particularly when combined with the casting techniques and metallurgy of the period. The Lincoln Y-block 368 was a 4 inch bore, I imagine limited to some degree by the spacing.

BTW, the comment in the article about 428 bore sizes on 390 blocks does NOT describe what tests he did to do it, you can almost guarantee a lot of blocks didn't pass the test, and that some that did still failed.

Sadly, there isn't a treasure trove of special FEs out there we can use.

[blykins]

I went through 2 once.  They sonic tested ok, but it was the pitting that got me.  Scrapped both.

[FERoadster]

I've got a C5 FE block that has been cross bolted but it's already bored +060 and needs a cleanup.
The attached sonic check shows me that I won't take it to +080 due to #5 and #8.
But I plan on using custom sized pistons from either Brent or Barry to make this a nice street engine with either a 4.25 or 3.98 crank.
I've got a couple of EDC engines that I may have sonic checked to see if they are somewhat thicker and a number of 105 blocks.

Richard >>> FERoadster

[falcongeorge]

I've got a C5 FE block that has been cross bolted but it's already bored +060 and needs a cleanup.
The attached sonic check shows me that I won't take it to +080 due to #5 and #8.
But I plan on using custom sized pistons from either Brent or Barry to make this a nice street engine with either a 4.25 or 3.98 crank.
I've got a couple of EDC engines that I may have sonic checked to see if they are somewhat thicker and a number of 105 blocks.

Richard >>> FERoadster

#5 is thick on the major thrust side, depending in the state of the water jackets, if that were mine, I would SERIOUSLY consider doing a fill to the bottom of the water pump holes, banging a sleeve in #8 and going to 4.13, but that's just me. That's a good block, almost all cylinders are shifted toward the major thrust side. You would still be well over 1/8 on the major thrust side in every hole except #8, one sleeve and its an excellent candidate.

[falcongeorge]

Whats ironic about all this is the OP is looking for an "early one". Hes looking in the wrong place