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401 to 425 specifications (Bore out?)


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If I bore out the 401 I have which is non correct for my 64 Wildcat can I achieve a 425 cubic inch motor?

Also I was told I have a 66 401 in my Wildcat. How do I decode the numbers located at the front of the block, near the valley cover?

Is there anyone who makes a 2x4 or single four aluminum intake that I can remove all raised manufacturers lettering - buff down and paint Buick green to look fairly close to stock on first glance?

Bryan

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I have heard that the 401 can be bored out to a 425, but it may make the cylinder walls too thin or break through if there was core shift. It is best to have the block sonic tested to see how far it can be bored. You may find .030 over is your best bet.

The 66 engines carried the M code on the passenger side valley pan rail. MT=401 4bbl, MR=400(401) GS Skylark, MW=425 4bbl and MZ=425 2x4. 65 engines carried the L code and had similar designations, but the 425 2x4 was LX - not LZ. Try <span style="font-weight: bold">this link</span> for more engine codes and information.

There are two after-market 2x4 manifolds for the 401/425. Offenhauser still makes a 2x4 (and 3x2), but it somewhat restrictive. Edelbrock made the B262 2x4 that is no longer available, but the most desirable for performance. If you are lucky enough to find a B262, it is going to cost you. I saw one go for $800 on Ebay.

There are no after-market single 4 bbl for the 401/425. The stock 66 425 Quadrajet manifold and Quadrajet makes a good improvement over AFB manifold and carburetor. The Quadrajet set up is still reasonably priced (for a Nailhead that is). Elelbrock makes several AFB replacement carburetors that fit the AFB manifold and flow 600, 750 and 800 cfm. There are also some people (Jim Burek for one from PAE) that mill and modify the AFB manifold to fit a square bore 4150 series Holley carburetor. There are also adapters to put the Holley on the AFB manifold. I had an 1/2" adapter for a 750 Holley that ran very well on my 63 Riv.

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<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I am told that you can not make a 425 out of a 401. Others can confirm this on a very active Yahoo group, Buick Nailhead.

Doug Cook </div></div>

Doug,

I thought the same way, but Carmen Faso told me it was possible, and that he had done it several times. If Carmen said it is so, it is so! That is why I don't bother with that site anymore.

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I hate to argue with the likes of such experience, but it seems to me... If it were that easy to make a 425 out of a 401, why are 425's so desirable and hard to come by when 401's are all over the place and only need a punching out?

I'll stick with a real 425.

But if one were to try that radical of a bore job, be sure to have the walls tested for thickness first!

Still learning,

Doug Cook

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<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I'll agree Carmen is one of the gurus for our Nailheads but I wonder how many of these motors had to be sleeved after boring.

</div></div>

I guess I should rephrase my original statement to read "I have heard that some 401s can be bored to 425s depending on core shift and cylinder wall thickness." Certainly not all or even most are candidates. It is still best to sonic check the block to see exactly how far you can go!

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I did not expect this much 'back & forth' on the issue of boring. It just seemed logical that the motor started as a 322 and the engineers kept 'boring it out' until it reached maximum capacity. I mean - how is a 425 made in the first place - is it a completely new casting forma 401? Or in 1963 at the factory don't they just increase the bore size? And so - the wall thickness of a stock 425 would have to be pretty thin to begin with I guess except that the engineers would not go so thin as to compromise quality and reputation in the field. So there must be enough wall thickness to withstand the rigors of 100,000 miles plus of travel.

But basically my question is answered. The extra cubic inches were derived at by boring. If I stay stock size (and I haven't done measurements yet) and the cylinders are true enough to require only honing - then that's OK - I'll need to figure out how to maximize HP in other ways.

Thanks for the input from everybody.

Bryan

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  • 14 years later...

Buick 350cu " small block weigh 450 lbs.  Baring core-shift [--sonic-test your engine ], a 350 can be bored & stroked to give 425-427cu. replacing the fallible aluminum water-pump cover that WILL warp over time/mileage with a steel/strengthened piece, find a buick 350 and bore/stroke it to 425cu.  This will take a bunch of careful machining and parts.  Consult with the big guys that do this to see what can be done.   The Pontiac block V-8 can go from 287-455, so why couldn't a 401 go to 425?   The later engines [--1968?] were thin-wall castings but STILL had a LOT of bore/stroke "room" baring core shift.  Thin-wall castings are why the later, larger engines had more displacement, and a hundred pounds or so less weight.   Check it--a Buick 455 weighs LESS than the Buick 425-430.   It's YOUR ride,--I think its COOL to put in any engine that'll fit, but a different one won't have "nailhead heads, so it might not "look"..." Buick"... of the era of your car.   

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  • 2 weeks later...
On 9/19/2003 at 8:04 AM, Guest said:

I did not expect this much 'back & forth' on the issue of boring. It just seemed logical that the motor started as a 322 and the engineers kept 'boring it out' until it reached maximum capacity. I mean - how is a 425 made in the first place - is it a completely new casting forma 401? Or in 1963 at the factory don't they just increase the bore size? And so - the wall thickness of a stock 425 would have to be pretty thin to begin with I guess except that the engineers would not go so thin as to compromise quality and reputation in the field. So there must be enough wall thickness to withstand the rigors of 100,000 miles plus of travel.

But basically my question is answered. The extra cubic inches were derived at by boring. If I stay stock size (and I haven't done measurements yet) and the cylinders are true enough to require only honing - then that's OK - I'll need to figure out how to maximize HP in other ways.

Thanks for the input from everybody.

Bryan

The 425 engine was a midyear introduction becuz they did cast a different block to successfully acheive that big of a bore size. Sonic testing is a very inexpensive to avoid taking anyone's advice on bore size capability. No brainer imho! But first look at the hp Buick itself advertised. 364" W/4barrel 300hp. 401" 4barrel 325hp. 425" again slightly higher, vs $. 455s almost start where Nails leave off hp-wise. Quality of structural engineering? Nails, skirted bottom end, forged crank & rods, oiling generally not an issue. I own both. Lots of research is needed to find fit for your use. If it blows up, build it better next time$$$. Lol!

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  • 1 month later...

When engine size increases, especially bore diameter, a different/upgraded block casting usually is involved.  A stroker motor needs additional clearance between the crank counterweights and the oil pan rail on the block and possibly the bottom of the existing cylinder bores (at the bottom).

 

ALSO be aware that when you use larger pistons, you'll need to get the motor "balanced" for them.  When a longer stroke crank is used, in an existing block architecture/family, that will automatically ALSO mean special pistons with a different piston pin location.  PLUS the previously-mentioned crankshaft counterweight clearance issue (done manually with a grinder and TIME).

 

I suspect you desire to "pull a sneaky", but for 24 more CID?  Work on the existing heads some.  Find a better camshaft.  Put a BETTER under-car exhaust system in place . . . 2.5" pipes with QUIET low-restriction mufflers.  The Q-Jets were rated at 750cfm, so that's plenty big for a good street motor, just find somebody that KNOWS how to work on them!  No need for a 2x4bbl system.  Back then, the 4bbls were more like 500cfm each, so adding another 250cfm with just a carb/manifold change would be much better and easier to keep running right than a 2x4bbl system, by observation.  A much better fuel distribution flow pattern, with the single 4bbl, too!  THEN . . . it should run well enough to tell everybody it's a 425 when it's not?

 

On DRAG RACE motors where they need huge cylinder bores, they usually pour concrete into the bottom of the water jacket for additional strength to back-up the thinner cylinder walls.  NOT for a street car!

 

Just some thoughts,

NTX5467

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