Couple of things to look for when shopping for a 400 block is previous overbore and core shift. First step is to look at the stamped block numbers to see if the block has had the deck surface milled - this would indicate a previous rebuild. Now if the heads are off you can measure the bore size themselves to check for overbore (and look for a step at the top of bore indicating bore wear). I say this because a common issue with 400 blocks is core shift and this can greatly limit the reboring of the block for rebuild. Which is the second item to look for - coreshift. Look at the lifter bores (if the intake is off) - if you can - and see if they are centered or not. Also look at the cam tunnel if the timing cover is removing and see if that is centered or not.

Well I have three 400 blocks now and found them all on Craigs List. Just be patient and keep looking for a standard bore block. I found 400 blocks at several swapmeets also but again make sure its still standard bore. I read you are in no hurry for a block so it should be more fun than frustrating.

So here's pic of one of my 400 blocks. It was already acid tanked and inspected so I paid top dollar for it - $400 of course. The next block I traded an nice GM intake for it and less than $300 - but had to drive 3 hours each way to pick it up. My last block was a long block and only $150 but had to drive 4 hours each way for that one.

Good luck and have fun with it.

400 standard bore block.

Lifter bores are mostly centered.

 

So is the OP, Claf lives literally right around the corner from me but has never acknowledged that on this forum...I've known him for 40 years.

Thanks or your offer but my plan is polar opposite from yours...I want to build a dead stock 406 short block with some cheap aluminum heads and a LT-1 -ish cam. Should be super streetable and have 400 HP.

The 350 in my car now is lucky to be pushing 300 HP.

 

I have to mention for a stock block a modest build is the better idea. For a hi-po build an aftermarket block would make more sense. A modest 400 (406) is just as easy to build as a 327 or 350" motor. 5.7" rods, solid lifter cam and modest performance heads a 400 block will still rock and roll.

 

GENERALLY, 1975 was the last year for the center freeze plug (it's been difficult to pin this down).
Then, ABOUT 76 (maybe late 75)-77/78, the 400 blocks had a boss for a center freeze plug. And then the 79-80 blocks had a smooth side in the center.

NOTICE VERY CLOSELY, on the sides of 400 ONLY blocks, BETWEEN the freeze plugs, the block sides have bulges from top to bottom of the blocks. The 283-327-350 blocks DO NOT have these bulges. I'm sure this was a casting change to enlarge the volume of the water jackets.

 

I agree with you. I'm just interested in the engineering challenge of achieving 427 CID with a stock 400 block. It's not about making big horsepower, but rather getting to the "magic" 427 displacement with a stock block. For some reason I think that a 427 small block would be pretty cool.

When I built my 383 a few years ago using a stock 327 block, I spent considerable time analyzing the things that limit how much stroke can be achieved in a 4-inch bore small block. The two key limitations are:

1) The clearance between the rods and the bottom of the cylinder bores
2) The clearance between the rods and the cam

Notice that the rods show up in both of the above limitations. What I learned from my analysis was that choosing the right rod can make a big difference for both of these limitations, although some rods are better at one than the other (block clearance versus cam clearance). Some rods are pretty good at both.

I've compared about 25 different rods for both block clearance and cam clearance. Two budget performance rods that are pretty good at both are the Eagle SIR and the Scat Pro Stock rods. These make it pretty easy to achieve 383 CID in a 4-inch bore small block. With the 4.125" bore and the bigger clearance notches of the stock 400 block, these same rods put 427 CID within reach in terms of block clearance.

However, since the cam height is the same in the 400 block as the 350 block, achieving 427 CID with a stock 400 block becomes a major challenge. The solution I have in mind is to use a performance rod with the smaller "big end" that typically comes with a smaller rod journal. My current favorite is the Callies Compstar rod with the 1.88" "Honda" journal that is popular for circle track racing. It appears that this rod will make it pretty easy to achieve 427 CID with a stock 400 block and an (almost) standard base-circle cam.

So yes, the cost goes up when using the Callies rods, and the cost goes up again for a custom 400 crank that has 1.88" rod journals. It's a lot more expensive to get 427 CID than 406 CID using a stock 400 block.

In terms of power production, it doesn't make economic sense to chase the added displacement. However, I'm interested in building a 427 small block just for the engineering challenge and the "cool factor" of a 427 small block. This project is on the back burner while I complete some other projects, but eventually I hope to build a 427 using the 400 block that I have on hand.

 

Didn't want to step on someone's ideas as the stock blocks can be modified for strength and even more so with today's newer technologies. But after welding in plates and cryogenic treatments the cost of an aftermarket block is more reasonable along with less effort. And to get a stock block to 427" requires a custom ground crankshaft of something like 3.93" stroke. Otherwise you really end up with something like 428" and that goes for the aftermarket blocks too. I read countless posts of 427's that are really a 428" or 426" so what's the point? In fact I try to avoid those discussions as it kind'a annoys me.

John Lingenfelter (RIP) long ago determined the largest best displacement for the stock 400 was a 420" with a 3.85" stroke and using 5.85" rods. The 5.85" rods will have less ring pack/ring seal problems and provide normal bore wear. Making a 427 out of a stock 400 block may make for nice conversation but the effort to get there and use/life of the motor is restricted/reduced.

Anyways enough of getting off the topic of selecting a 400 block. Just wanted to share what I look for in shopping for a 400 block and not what to build it for. I think a stock 400 block can make good sense for a performance replacement unless you want to get fancy.

 

I agree that a stock 400 block (4.125" standard bore) is just as easy to build as a stock 350 block (4.00" bore). And, the increased displacement automatically offers more TORQUE, regardless of what you choose for cam, compression, heads, and intake. For general-purpose street engines, torque is what really makes a car feel powerful. Peak torque is roughly proportional to displacement, so in this respect, more is always better.

Just as a 350 block can be easily stroked to 383 CID, the larger bore of the 400 block makes it easy to stroke beyond 400 CID. Some people think the practical limit is 420 CID, but I think the Callies 1.88" journal rods make it easy to go to 427 CID or even beyond that.

I'm involved right now helping someone use the Callies 1.88" rod to build a 396 CID engine based on an original 1965 '870 327 block. The same principles make it possible to achieve 427 CID with the larger bore of the 400 block.

For people who already own a complete 400 short block, the easiest and lowest-cost path forward is to just rebuild the 400 with a small overbore to clean up the cylinders. However, if all they have to start with is a bare block, and they have to purchase a crank, rods, and pistons anyway, there is an opportunity to stoke the engine beyond 400.

As DZAUTO has described in other threads here, getting to 420 CID is economically quite feasible. Getting to 427 CID costs more and the power difference in negligible, so most people should probably settle for 420 CID maximum. I just happen to like the challenge of reaching 427 CID.

 

In past years, I've built two 383 engines using small journal 327 blocks blocks. BOTH were line bored to 350 main journal size and a PURE, BONE STOCK 400 cast crank was used with the mains (2.65) turned down to 350 size (2.45). The bottoms of the cylinders were notched---------------------------JUST ENOUGH for rod clearance---------------------NO MORE.
I've also built two 350 engines from a small journal 327 block. The mains on the 350 crank were turned down to 327 size and the diameter of the flange between the rear main journal and rear seal journal was cut down to fit into the grooves of the block and cap. Bored .030 and build it just like any 350. TOOOOOOOOOOO EASY!
IF, IF, IF a 4in bore block has enough wall thickness (determined by sonic testing), it can be bored to .060in over. This results in 389 with a 3.75 stroke. Now, you can go one step further and OFF SET grind the rod journals down to small journal size (2.00 or even 2,010 giving a 2.85/2.86in stroke) and gain even a little more stroke, which will result in over 390cubes. BOTH of those engines got bone stock 66-67 327 rods that were shot peened, resized and got ARP Wavloc bolts. The bolt heads were lightly clearanced at a 45deg angle for cam lobe clearance. More stroke, more torque, more real world usable power on the street. Add to that, a high geared rear ratio (ie 3.08, 2.73) and a WIDE ratio tranny (NO automatic!!!), and the result is a nice driver, Interstate cruising and improved fuel economy.

Back yard, shade tree, poor boy from the wrong side of the river, stuff??? Yes sir, that's right! BUUUUUUUUUT, some of this kind of stuff was gleaned years ago from HOTROD magazine (and others) articles (back when it was a GOOD mag with real world, usable tech articles). And yes, I do own cars (and a boat) with examples of this kind of home made, back yard engines-----------------------and they all work damn good!

The days of zipping around with a high winding 283-327 and a 4.11 or 4.56 rear are over!

 

Hi Tom:

As I recall, you also built a 420 using a 400 block. Can you refresh me on the combination of stroke and rods? I'm particularly interested in what you did about cam clearance.

Also, was the cam a flat-tappet cam or a roller cam?

Thanks,
Joe