[grandville455]

This ^^^^^

[GRX]

Why this isn't a Sticky already?

[Nicks67GTO]

Read through it in patches and I saw all the think and thin web pics. I have a question though.....

Are we saying that the 67' blocks are one of the better starting points or not so good starting points? I ask because I have an uncut 67' big car block laying around I was planning to use for a KRE headed stroker in the near future....

[gavin]

1962 block 538181 used for everything from 389 2lb to 421 SD.For comparison a 1969 wz 400 block. the 62 block weight is 187lbs the 69 block weight is 177 lbs. note the main caps.

[gavin]

Some more photos.

[chiphead]

Nick- The '67-'71 400 blocks are the best. They have the most meat in the main webs and supposedly had more nickel in the cast iron alloy. Even the '67-71 2-bolt main versions are stronger than the blocks made '75-79.

[GRX]

The nickle content thing is an unproven myth far as I know. Far as the advantage of '67 blocks, see my post #'s 156, 157, and 158 above.

[LPI]

The 1967 and 1968 2 bolt main blocks are very similar in structure and strength.

In 1969 they started decreasing the material in the webbing and continued doing so each year there after. If you set up a 1967, 1968, 1969, 1970, 1971, 1972 and 1973 blocks each one will have subtle changes in the main webbing area. In all cases the webbing gets thinner as the year of the block gets newer.

Another item to watch out for is the letters stamped on the oil pan rail. If there are letters stamped by the main cap webbing on the oil pan rail you better measure twice and cut once or you will be sorry. Again another item that gets blamed for engine/bearing failures when in most cases it is a measurement error.

I have the revision list from 2/69 thru 7/72 which shows most of the changes and updates over the years on these 9799 thru 485 blocks.

The actual material used was Cast Iron - G.M. 232-M

One of the reasons why the main caps break or crack at the dowel pin hole is from switching from factory bolts to ARP/Milodon studs. Studs and 4 bolt mains are not better unless you look at all of the parts and each individual application.

Another note. GM did not use "standard" diameter dowel pins in the main caps.

[LMSRACER]

Originally Posted by LPI

I have the revision list from 2/69 thru 7/72 which shows most of the changes and updates over the years on these 9799 thru 485 blocks.

The actual material used was Cast Iron - G.M. 232-M

One of the reasons why the main caps break or crack at the dowel pin hole is from switching from factory bolts to ARP/Milodon studs. Studs and 4 bolt mains are not better unless you look at all of the parts and each individual application.

Another note. GM did not use "standard" diameter dowel pins in the main caps.

For those that don't know, He's talking about the 455 Block when he says "9799 thru 485".

Also, for those that don't know, the Pontiac Dowels are 0.3095" and NOT 0.3125" (5/16").

[LMSRACER]

Whenever I'm building a 400 Block Based, Performance Engine, I look for Blocks that haven't been drilled or tapped for four bolt main. This way I can install Splayed Caps on the Center Three.

Also, whether I'm building a 400 or 455, I prefer a Block without Cylinder Bore Chamfers. This way I can put the Chamfers where I want them. That's the problem with the '67 400 Block, the Bore Chamfers are too large and they are in the Wrong Place for '68 and newer cylinder heads. (Some '67 Cylinder Heads Too.)

As for the Main Webbing Issues, that is more of a 400 Block Issue than a 455 Block Issue. In almost every case, the 455's Main Webbing is much thicker than the 400. Look for a 1970 to 1974 455 Block.

The 400 shines in the "Less Likely to Crack Down the Center" department because the 400 is 1/8" (0.125") thicker from the edge of the Cam Bearing Tunnel to the Edge of the Main Bearing Tunnel. This is of course due to the 3.00" Mains in the 400 compared to the 3.25" Mains in the 455. Again don't confuse this thickness for an Increase in "Main Webbing" Thickness. They're NOT the same thing.

The Cast #481988 400 Block that hasn't been Drilled for Four Bolt Main is a Good Candidate for a Performance Build. Although the Main Webbing Does Vary from Year to Year.
The Cast #'s #9799140 and #485428 455 Blocks are good Candidates for a Performance Build. I actually have a #485428 that was never Drilled for Four Bolt Main and now has Splayed Steel Main Caps on it. It was Engine Code "YC" to Start with and it's Date Code is B221.

To Wrap it up, with all of that being said, In most cases the Cylinder Wall Thickness is what Varies the Most..... Once you locate, what you think is the "Right Block", it very well may have Thin Cylinder Walls. Sonic Testing ALL used Blocks is a must.....

Have a Good One,
Larry S.

[LPI]

Originally Posted by LMSRACER

For those that don't know, He's talking about the 455 Block when he says "9799 thru 485".

Also, for those that don't know, the Pontiac Dowels are 0.3095" and NOT 0.3125" (5/16").

I am referring to the factory Pontiac "block Cylinder" drawing and OEM specifications for the design of block 9799914, A 400 block. The subsequent designs and revisions which happens to be the base design drawing for a base block (which happens to be the 400 CID) and subsequent changes including the following blocks 9799915, 9799916, 97999140, 9799141, 481836, 490132, 485212.

Each block casting number received an additional drawing outlining details for that particular block. This print 9799914 is the basis for the castings and design intent for the 1970 production 400 blocks and 455 blocks. Hence the reason for reference to the two casting prefixes.

Here is a 1968 400 casting 9790071 fitted with 5/16" dowel pins and piloted washers in the main caps to be used with ARP main studs.

[LPI]

[QUOTE=LMSRACER;5335556]
As for the Main Webbing Issues, that is more of a 400 Block Issue than a 455 Block Issue. In almost every case, the 455's Main Webbing is much thicker than the 400. Look for a 1970 to 1974 455 Block.
[QUOTE]

Can you explain how you come to this fact based on two major differences in amount of material in the block casting, a 455 has larger mains and a larger bore. In most cases the 455 blocks where drilled if not drilled and tapped for the outer 4 bolt main bolt holes, again a decrease in material and strength.

What main webbing on a 455 is specifically thicker than a 1967-to 1969 400 block.

I would like to learn what block castings you are specifically referring to and what specific area of the block are you referring to as being thicker. Would you please post a picture or a casting number that you are referring to.

[LMSRACER]

Originally Posted by LPI

I am referring to the factory Pontiac "block Cylinder" drawing and OEM specifications for the design of block 9799914, A 400 block. The subsequent designs and revisions which happens to be the base design drawing for a base block (which happens to be the 400 CID) and subsequent changes including the following blocks 9799915, 9799916, 97999140, 9799141, 481836, 490132, 485212.

Each block casting number received an additional drawing outlining details for that particular block. This print 9799914 is the basis for the castings and design intent for the 1970 production 400 blocks and 455 blocks. Hence the reason for reference to the two casting prefixes.

Here is a 1968 400 casting 9790071 fitted with 5/16" dowel pins and piloted washers in the main caps to be used with ARP main studs.

I was under the impression that you were referring to the Cast #9799140 455 Block and the Cast #485428 455 Block.
Now that you have elaborated on your original post, I understand fully.

Larry S.

[LMSRACER]

[QUOTE=LPI;5335591][QUOTE=LMSRACER;5335556]
As for the Main Webbing Issues, that is more of a 400 Block Issue than a 455 Block Issue. In almost every case, the 455's Main Webbing is much thicker than the 400. Look for a 1970 to 1974 455 Block.

Can you explain how you come to this fact based on two major differences in amount of material in the block casting, a 455 has larger mains and a larger bore. In most cases the 455 blocks where drilled if not drilled and tapped for the outer 4 bolt main bolt holes, again a decrease in material and strength.

What main webbing on a 455 is specifically thicker than a 1967-to 1969 400 block.

I would like to learn what block castings you are specifically referring to and what specific area of the block are you referring to as being thicker. Would you please post a picture or a casting number that you are referring to.

The way that I come to this conclusion is that I have Ten Blocks here. I have '67, '69, '71 and '73 400 Blocks. Casting #'s #9786133, #9790071, #481988 and #481988 in that Order.
I have a Cast #9792968 428 Block.
I have a #9799140, #485428 (1971), #485428 (1972), #485428 (1972) 455 Blocks.
I also have a Cast #488986 350 Block (1974).

When a Say Thicker in the Main Webs I mean Below the Dowel Pin and Outer "Drilled" Bolt Hole Area. I Find that the #485428 455 Blocks aren't "Undercut" in this area at all. EVERY 400 Block that I have is undercut to some extent. This is where they Fail and this is what I'm concerned with.

The other place that Pontiac Blocks tend to Fail is Through the Oiling Hole to the Cam Bearing Tunnel. The 400 is "Theoretically" Stronger Here, of Course Due to the Difference in Main Bearing Journal Diameter and the Greater Amount of Cast Iron between these Two Points. I say Theoretically because often times this area of the Block is Cast "Thinner" in Areas between the Main Bearing Tunnel and Cam Bearing Tunnel.

I can Post Pictures if that won't Suffice.....

Have a good one,
Larry S.

[LPI]

Yes I would like to see a picture to understand where you are referring to the "undercut " area of a 400 versus a 455.

I am not trying to dispute what you are perceiving what I am trying to create is a dialog of factual documented information to help the rest of the Pontiac community make better decisions for spending their hard earned money.

[LMSRACER]

Originally Posted by LPI

Yes I would like to see a picture to understand where you are referring to the "undercut " area of a 400 versus a 455.

I am not trying to dispute what you are perceiving what I am trying to create is a dialog of factual documented information to help the rest of the Pontiac community make better decisions for spending their hard earned money.

I agree completely. I only post information for the purpose of being helpful.

Undercut isn't accurate since there isn't actually a machining process performed. It's more of a Thinner Area in the Webbing that was Cast that way.

I'll Post some Photos in the Morning.

Have a Good Evening,
Larry S.

[wolf]

lots of good info in this thread, and makes me feel more confident in my 485428 blocks. Question that I haven't seen answered here yet is how the '65-66 389 blocks compare to the '67-68 400s?

[gene simmons]

Originally Posted by LMSRACER

I agree completely. I only post information for the purpose of being helpful.

Undercut isn't accurate since there isn't actually a machining process performed. It's more of a Thinner Area in the Webbing that was Cast that way.

I'll Post some Photos in the Morning.

Have a Good Evening,
Larry S.

Is this the area on a 1968-69 block?

[BruceWilkie]

fwiw... my 59 block had been "built" sometime in 62... someone paid attention to details at the main bearing/cam feed holes.
A few yrs ago cleaning up a 69 400 block I noticed the cam bearing feed holes had a distinct sharp step in size(smaller) before the cam bearing...checked a 73 455 block I had and it too had the same step in size.

My 59 doesn't have this step... don't know if factory did it that way or if it was done back when it was "built" in '62. (The cam bearing itself has smaller oil hole anyway and ultimately is the metering "jet", so I don't know why factory stepped the feed hole in the web.)

I don't care for sharp edges... Seeing stock blocks tend to crack up the main to cam right up this hole I don't like the idea of having a possible stress riser there.

[70 bird]

STICKY THIS THREAD!!