[Skip Fix]

But do the blocks fail in the lifter valley that don't have that vertical rib? The ones I've seen fail with rollers break alot lower. Or is it if they have those they are meatier in the other areas also??

The far right looks like my 72 HO block.

[Tom Vaught]

Brian has given you part of the clue on the 3.25 main blocks.

The question now is "Is it the full length 1/8" ribbed block or the 'Dashed" block. LOL!

Tom V.

[Larry Navarro]

"holy four-bolt batman!........."
okay so we've got "clues"............now address Skips question.

[Tom Vaught]

Skip's question was on 400 Blocks. I have already posted my opinion on the 400 block, Larry.

Tom V.

[PONTIAC DUDE]

Brian, Brian. LOL. Wonder Who gave you that info.

The ribbed for your pleasure only applies with 455's.

The 400 are a totally different ballgame. There is no secret numbers or code to look for.

FWIW I have a coded RA IV block that I'm working on that doesn't have the support of a later 400 block.

Ya just have to have a supply of blocks and after awhile you will notice differences and what to look for.
This can go on for-ever. LOL.

Personally, I have found 4 different basic castings, as far as main area support, for all 400 Pontiacs.

[Larry Navarro]

Originally Posted by Tom Vaught

Skip's question was on 400 Blocks. I have already posted my opinion on the 400 block, Larry.

Tom V.

....but evolved into both blocks. If the none of these differences exist in a 400, then he questioned the integrity of the 455's.

[Brian Baker]

Originally Posted by PONTIAC DUDE

Brian, Brian. LOL. Wonder Who gave you that info.

The ribbed for your pleasure only applies with 455's.

The 400 are a totally different ballgame. There is no secret numbers or code to look for.

FWIW I have a coded RA IV block that I'm working on that doesn't have the support of a later 400 block.

Ya just have to have a supply of blocks and after awhile you will notice differences and what to look for.
This can go on for-ever. LOL.

Personally, I have found 4 different basic castings, as far as main area support, for all 400 Pontiacs.

Some "dude" in Florida that changes his mind about what car he is going to race as often as he changes his underwear gave me that info.

My 1975 455 block had those ribs that we're talking about...the "clue" in that picture. With splayed billet caps and a fill to the water pump holes, that block has lived at 800-HP. But a light reciprocating assembly is a must. Running this kind of power in a factory block with steel rods, in my opinion, is asking for it.

[Skip Fix]

Overall original question was 400s, but alos tips on 455s. As Ken mentioned the changes are subtle and unless you have alot of blocks to look at next to each other9or pictures here ) to my eye it is tough to see the difference.

Similar question on the thick pan rail , do blocks actually break there? I thought it was mainly lifter bore with big rollers or main webbing esp #2.

My question is -does the rib help lifter valley integrity or do they just "indicate" a block that is beefier all around? ? Usually the lifter bores themselves break out well below that, that I have seen and these ribs to me look like they would not help that at all. So

[David Holmberg]

Looks like I'm the only SOB here that can keep his word...

Mongo = Blabbermouth...

[Brian Baker]

Originally Posted by David Holmberg

Looks like I'm the only SOB here that can keep his word...

Mongo = Blabbermouth...

Nobody really cares anymore, David. At least that's the vibe I get from Ken.

Skip, on the pan rail deal...think back to the early blocks that had that reinforcing rib. It beefens up the thrust side of the main saddle area of the block. I can't imagine why Pontiac engineers decided to do away with that rib in the rail, except to save money in casting, figuring for the HP and durability issues the engines would see, they didn't need it.

Yes, they do tend to split up the middle into the lifter valley area (ie - between the mains and the cam bearings). Think of our V8 as two four cylinder inline engines linked together in a V, with the two of them pulling apart from one another, stretching the link. That's what causes the splitsville up the middle. When compared to other GM blocks, again, maybe the engineers didn't feel more reinforcement in that area was needed for the HP and durability they would be exposed to...that is until the R.A. V program.

[Skip Fix]

But to me it looked like those ribs ran up from the lifter bore to the deck, not across.

[69*Goat]

Skip.....

I have a great example of what could happen to that block that you posted pictures of if you decide to high hp it. As a matter of fact, it is making a great boat anchor right now.

[Brian Baker]

Originally Posted by Skip Fix

But to me it looked like those ribs ran up from the lifter bore to the deck, not across.

Skip...re-read my last post. I was addressing your question about that reinforcing rib that used to run parallel to the pan rail.

Those other ribs do run from the lifter valley to the deck. In and of themselves, they do nothing to strengthen the block, but on a 455, they are a clue to a block that has beefier main webbing than a 455 without them. Clear as mud now?

[75TA]

For comparison here is an IAII 3.25 inch main block webbing. Just posted so one can compare to what is suppose to be the best block.

[Skip Fix]

That's what I thought Brian.

Just the more pictures to show the subtle differences I think would be great for those building moderate performance motors.

My current project is an aftermarket block as I HOPE it will make enough power to have broken even a good factory block! we'll see hopefuly soon. Cam's degreed, Finally have re engineered the Crower shafts for them, just need to set the height this weekend. Button a pan on it and light her up!

[GRX]

A lot of talk about block thickness but none of how the molds are structured as of yet. The location of the mold parting lines can have a very significant effect on the "skeletal structure" of the overall casting. The way the mold parts are arranged can also have a very significant effect on strength since it effects how the molten metal flows through the mold when it is poured.

As we all know, the core for these blocks consist of many parts. The mold is not just one big unit but must be made in pieces to allow removal of the casting afterwards, and also to allow for location of extraction pins, hot gas escape ports, etc ... etc ... The resulting lines between the core parts are refered to as the "parting lines", and usually result in a less consistant grain structure in the area.

OK ........ on to some images ............

Here we compare my 1967 400 block to the 1975.

1st image = '75 block. Please note the orientation of the parting line maked red.

2nd image = '67 block. Very different orientation wouldn't you say?

The third image is another view of the '75 parting line. There are many images of later castings which cracked right along that vertical line up to the main cap. The '67-'69 arrangement places the parting line much farther away from the main saddles.

[GRX]

Another comparrison of parting line differences - this time at the bottom of the cylinders.

1st = '67 block. Notice the horizontal parting line below the cylinder.

2nd = '75 block. No such parting line.

Also notice how the boss cast for the motor mount is tied into the main in the '67 block vs. the '75 block. This is common across the entire block as you can see from the 3rd image.

[GRX]

And another mold parting line comparrison. This time we are looking at the rear passenger side of the block.

1st = '67 block

2nd = '75 block

In my humble opinion, Pontiac very likely changed over to the later set up for cost savings since the earlier design looks to be more complicated to work with.

[Skip Fix]

Here's a 72 HO block added to the pictures.

[Tom Vaught]

GRX, thanks for the pics.

So far there have been three things posted in the pics that made the 67 400 2 bolt main the block to use for Marty's deal.

1) Much more material in the main webs on the non drilled 67 2 bolt main block vs the 67 4-bolt main block (We all know that a splayed cap into the pan rail is stronger than the 4-bolt vertical cap deal). Heck! The K+M boys are recalling all of their 4-bolt main vertical cap blocks for the reason I just mentioned above.

2) If you look at the valley area on the 67-70 type 400 blocks you will see wide raised pads in the valley area. This extra material strengthens the block both top to bottom and left to right in the upper part of the block.

3) Last but by far not the least GRX got around to posting about the casting change that affected how the block was poured and cooled. Remember the Soft blocks that could have had casting issues due to the cores not being right on the cooling after they were poured? Cooling has a great effect on how strong a block is.

Early on he was going to post the pics and I thought the deal would come out then but it took him til now to get around to it.

Those are the reasons why I picked the 67 2-bolt main block.

By the way, Marty also had the block vibrated to remove any stresses trapped in the material before he built it up and the block did have a lot of years of thermal cycling as a used engine.

Tom V.

ps A 3" main will always have more support in the main webbing vs a 3.25 main block which is why it still is better vs any 67-later 3.25" main block for strength.