[pippintook]

w72

[pippintook]

w72 valley pan shot

[455-4+1]

Good pictures

So does anyone have pictures of a "thin web" 400" block for comparison so we are certain where to look to locate the differences ???

Can the XX casting designation be used soley to identify a "Good" block ?? (Actual block condition aside)

Are these blocks as good as the early 400" or lesser inch engines for an endurance type build
(5500-6500 rpm for 50-70 seconds ??)

Sorry for all the questions just trying to get some notes for 400" blocks

[Ray Cox]

I think my spare motor has the casting marks like that. guess I need to check

[Half-Inch Stud]

MFC...nice Main Cap Bolts.


yea....let's kee the Main Dowels Solid. Until maybe a fancy-development-racer guy can find that a single roll-pin & single solid pin on #2 cap is a secret fix to splitting blocks.

I propose that the Roll Pin be used on the Head interface. Afterall Aluminum Heads could use it, and my 48's would not sit onto my 455 because of the solid pins...si I reamed the HEad hols (THAT WAS A FIRST).

HIS

[pippintook]

This is a quote from Jim Hand's book, How to Build Max Performance Pontiac V-8s:
.
"...as part of the weight saving program, the 400 blocks were redesigned with lighter main saddles and thinner cylinder walls during the mid 1975 production year. Included in this group are casting numbers 500557,XX481988 and 568557. These blocks may not have all the holes drilled for various engine mounts used in earlier model vehicles, and all should be carefully inspected to assure the mounting holes match your intended application. For high performance, higher RMP applications, earlier production blocks are preferred.." (Chapter 2, p.22).
.
So, does the XX481988 block have lighter main saddles and thinner cylinder walls? Does that mean the XX481988 block is not a revamp (ie. basically, the same) as the 71-74 400 block 481988? Is it possible via visual inspection to tell how a 400 block has lighter main saddles? Does anyone have any pics of 500557 or 568557 blocks for comparison? Why did Pontiac use the XX481988 block?

[Rocky Rotella]

MFC, I am to blame for the slightly misguided information in Jim’s book.

At the time the information was gathered (over a year ago), we were lead to believe the XX481988 was a thin wall casting. In speaking with a former Pontiac engineer who was directly responsible for developing the 500557 block to lighten the castings, he stated directly to me that main saddle and cylinder wall thickness was significantly reduced also reducing the integrity of the block. He stated that at that time they were not used for super high performance and high rpm applications and strongly suggested staying away from them for high performance use.

When asked about the XX481988 block, he said that they did have crankshaft and/or block problems related to the thinner main webs and that they may have reverted back but he said the early blocks were still better in his opinion. We have since found that they may indeed be identical to the early 481988 blocks but they are still missing the motor mount holes, which are nothing to drill/tap.

I think Paul Spotts can provide any specific information about the blocks. Paul, have you sonic checked a bore? Is the nominal thickness the same?

[Paul Spotts]

Hi Rocky - thanks for that info. very interesting.

I never sonic checked a bore on the XX as I never went past .030 bore. I did compare the XX block with an earlier one (same casting number and they appear to be identical

The fastest way to id a thin web block is to check the main cap bolt threaded holes - the thin web blocks go all the way through - the thick web blocks do not - in other words the thick web blocks have "blind" holes and the thin do not since the thin blocks lack the material. In comparing blocks it is also very obvious that the "web" or metal under the area the caps mounts to, lacks material.

The thin wall blocks I've built all had issues with caps being out of alignment - I wouldn't use them for a stroker conversion or any performance usuage.

[455-4+1]

Thanks Paul. Good description