Later model 400 blocks
 

I am looking at Pontiac 400 block that is out a 77 that is for sale. A couple hundred is the price. I have a 74 350 that came with my 76 Formula and is out of the car. The issue with the 350 as you know is availability of pistons. Plus it is a smaller motor. Just thoughts on the later 400 as I know the block is weaker. I have a set of big valve 16 heads and I was planning on a street motor for the car. I see the piston selection is much larger for the 400. This car is basically going to be a street cruiser with 3:23 gears and I plan on having the A/C working and all. Wonder some thoughts from you more experienced guys on the 400 ?

Yes, there is some concern over the later blocks with casting number ending in 557. It is said that they have thinner casting and are therefore weaker than the earlier 400 blocks. I know from experience the 400 block in my '77 Grand Safari Wagon lasted to 165,000 miles, when it needed a valve job. I would not hesitate to use the engine you refer to.

For your purposes the '557 400 block will be just fine. Just have a competent machine shop go through it for you and slip a mild cam in it and you'll be happy motoring.

The 557 blocks absolutely are thinner and weaker than earlier castings.

But, as said, they're fine for mild builds. Just be sure to magnaflux it and look for cracks at the dowel pins in the main webs.

Lack of 350 pistons is a baseless tale.
Sitting on a shelf yes.
Impossible to order no. Might have to wait a few more minutes and spend a few more $$

It's a cruiser enjoy having the original stronger block less structural worry about it flying apart (priceless) and slightly better mileage.

.

I would NOT use a 557 block for a stroker project for any reason. It's been at least 15 years now but a member of this Forum did exactly that. He built a relatively "mild" 455 based on the later 557 block, iron heads, RAIV size cam, about 10 to 1 compression. It didn't last very long at all, cracking the block where the main caps bolt down. The early blocks are still out there, I just sold two recently, I'm sure there are a few still around in your area if you do a search for them.........

hes not bulding a stroker...

a 557 block is perfectly fine for a low hp street cruiser. if youre building it to 400+hp &/or racing or abusing it then find an earlier 400.

My RAIV headed 400 used one I hammered on for 10 years roughly 400 HP. I think Tom S had one as a dyno mule that made more. So for even a mild warmed over cruiser should be OK.

I appreciative of all the inflormed folks here that have warned about the "potential" problems with the thin block. I remember several times that Ken Keefer communicated that those blocks were OK for mild builds. His real life engine building experiences were huge (just like Cliff and others here).

All the pictures I've see of those blocks that broke, a crack either generated from a dowel pin hole or the oiling hole in the main web. I would chamfer those holes on a thin block, and de-burr the whole crankshaft/main webbing area and have it checked for cracks, first...

Why not just locate a earlier 400 in case you want to step it up more down the road ? Even now they don’t seem to be rare.

Back in the day my buddy ran low eleven's with a stroked 557 block build and mid tens on spray. It was raced for several reasons and never failed.

I've seen the "Google" pictures of blown up 557 blocks and all I can say is "engines fail for a reason". More than likely something else was going on before the 557 block imploded.

FWIW.... Butler rates the 557 block good for a 600 horsepower limit.

Couple reasons maybe;

Original engine to the car.

Already have the block and it will work for the intended build.

To me, using a "557" 400 block in place of a 350 Pontiac is a no brainer. Even though pistons are available for a 350, at a greater expense and effort than a 400, what do you have when your done? A 350 Pontiac engine vs a 400. Even with a very mild build, you are giving up 40-45 "free HP", by virtue of the displacement. More importantly, you are giving up 50-60 Ft. lbs. of torque, power you can feel seat of pants. The physical engine size is the same, so why build a 350? To keep a numbers matching combination together or because a specific race class requires it would be the only reason to keep the 350 IMO. Gas mileage improvement would be in the 1 to 1.5 mpg range if that's really a consideration. The 557 block is not the best 400 block, no question. But for a 400 HP or so stockish build, I would have no issue at all using one. I would think you would enjoy having the very real increase in power with no downside. Good luck with the build.

LOL, or one of the 455 blocks you are hoarding:eek:

I built a 557 block, but looking back I should have just kept the low mileage 350 and added a centrifugal supercharger. It would have been more power and less expensive than building the 557 block. It also would have been cooler than a plain Jane 400.


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For a street cruiser, there is absolutely nothing wrong with using a 557 block. With that said, good standard bore non-557 400ci blocks can still be found for $500 fairly easily. If it were me, since you're going through the trouble of building a new engine from the ground up, I'd pay the few hundred extra dollars to get an earlier 400ci block that will give you the freedom to increase power if you ever want to down the road.

There's been some questions about whether or not, a light weight 350 was produced (possibly).....
Not sure there's been a definite answer on that.
BUT a light weight 455 has never been known, although I've read some subtle differences in those blocks, also

They are not good for anything other than a dead stock 200HP late 70 'wheezer" build.
My buddy built a nice little 400 with one. RAIV cam, home ported 62s, forged 5140 rods and TRW flat tops. It ran low 11s in a 70s Formula.
It ripped every main out of the block. The crank almost got shoved right out of the bottom of the block.
Shifted at 5800, not abused.
Do not waste your time.

My original 557 block in my 78 T/A had 12 heads, balanced and blue printed with TRW flat tops, an Armasteel crank and a RAIV cam .
As I was about to shift into third at WOT that motor came apart like a $2 watch. It was reliable for years before that. All the webbing between the mains and cam journals were hollowed out. The crank snapped in three places and the camshaft in four. What a waste of a good crank!!!

Now you’ve started a rant, but that has more to deal with moron buyers than anything. About 12 years ago I put a lot of garden variety 455 engines up for sale that the blocks and cranks were checked for cracks and I guaranteed them in writing. I think I wanted $500 each complete with your choice of complete heads including 6x ones.
I had so many time wasters and lowballers asking the most asinine questions that I finally just gave up. It just wasn’t worth my time and I also started disliking strangers coming to my home where I started wondering if they were just checking out my house and stuff where I also had my wife and kids.

I can tell you this :
Every 455 I’ve had that was 2 bolt was drilled & tapped for 4 bolt mains and I have a few 1975 & 1976 blocks. There was a rumor that there was some very thin walled blocks out there that were sketchy at .030” but every one I checked was safe for .040 “ at least and the 1970 455 block in my GV could have gone .060” +