LS4 Cylinder Block Casting Number

[George H.]

^rd Edition.

George Hunt
'73-74 TM 3rd Edition Team Member

[Joe L.]

Re: LS4 Cylinder Block Casting Number

^rd Edition.

George Hunt
'73-74 TM 3rd Edition Team Member

George-----

Are you sure it's a "P"? I've never seen or heard of that foundry code on any GM casting, let alone a Tonawanda casting which are usually "T".

GM's Defiance, OH foundry started casting big blocks after the Tonawanda foundry closed but that was well after 1973. As far as I know, Defiance did not use a foundry indent code. In fact, I toured the Defiance gray iron foundry many years ago and asked about their foundry mark. They looked at me quizzically like "what's that"? I didn't see a foundry mark on any of the castings I viewed there.

[George H.]

Re: LS4 Cylinder Block Casting Number

Yes, there is a "P" stamped on the block. "See attached picture I just took." There is a GM T12 and below that: 3999289 (vertically) and to the right of that block number, "P".

I am asking what the P stands for. Also, T12?

George Hunt
'73 LS4 / M21.
3rd Eddition 73-74 TM Team Member.

20231219_170524.jpg

[Owen L.]

Re: LS4 Cylinder Block Casting Number

Yes, there is a "P" stamped on the block. "See attached picture I just took." There is a GM T12 and below that: 3999289 (vertically) and to the right of that block number, "P".

I am asking what the P stands for. Also, T12?

Not 100% but I've always believed the cast-in P indicates "passenger" and the T12 could be the pattern identifier in case a defect crops up in the castings.

[George H.]

Re: LS4 Cylinder Block Casting Number

Thanks Owen, that makes sense. We need to add wording to our '73-74 Tech Manual (4th Edition TBD)

George Hunt

[Patrick B.]

[George H.]

Re: LS4 Cylinder Block Casting Number

Ok, I'll accept that. So the question is now, what does the T12 stand for? Are all 1973 LS4 blocks stamped T12? A 454 cu block was an engine option for all Chevrolet cars and trucks in 1973, not just a Corvette. More 1973 Chev "trucks" were sold with a 454 than 1973 Corvette. I'm not sure those blocks were stamped "P".

George Hunt

[Keith B.]

Re: LS4 Cylinder Block Casting Number

that is embossed not stamped.

[George H.]

Re: LS4 Cylinder Block Casting Number

The wording in our 73-74 Tech Manual for all casted parts showes to as,"stamp information." Maybe it shoudl be embossed. But to emboss something, you first have to stamp it. Yes the numbers are embossed. Thank you.

George Hunt

[Mark F.]

Re: LS4 Cylinder Block Casting Number

Not 100% but I've always believed the cast-in P indicates "passenger" and the T12 could be the pattern identifier in case a defect crops up in the castings.

I agree with Owen.

T12 is most likely a pattern/mold number (male) which is then transferred to the sand mold (female) when the sand mixture is compressed in the mold frame. When the molten iron is poured and fills all the casting cavities, the resulting number you see (male) on the casting is referred to as "embossed" as Keith said.

Sounds like they made a lot of these puppies, so they do wear out; get repaired occasionally (if possible); and then get retired when they are too far gone and not used again; etc. So, there may be T13s, T14s etc. - I don't know just speculating.

[Patrick B.]

Re: LS4 Cylinder Block Casting Number

I agree Mark. That Txx number was a pattern number for the wooden form that was used to make part of the sand mold. There were several, so the blocks could have different pattern numbers in various parts at random. Only the casting number and the date casting are of interest in identifying blocks.

[George H.]

Re: LS4 Cylinder Block Casting Number

Good follow up Mark. I understand its not a judging points issue, but, only a what the X do the embossed markings represent? Is this the case on all "T" C2, C3 big blocks? No mention in '73-74 tech manual regardeing these markings.

George Hunt

[Terry M.]

Re: LS4 Cylinder Block Casting Number

Good follow up Mark. I understand its not a judging points issue, but, only a what the X do the embossed markings represent? Is this the case on all "T" C2, C3 big blocks? No mention in '73-74 tech manual regardeing these markings.

George Hunt

Not only Tonawanda castings, but Saginaw castings as well. I would think it is the practice all across the casting industry and mold numbers will be found on castings of other automobile makes. Probably on castings for appliances as well - at least back when appliances were made of iron. it is simply a means of tracking sources of castings for quality control purposes.

[Owen L.]

Re: LS4 Cylinder Block Casting Number

A cursory google image search for 3999289 engine pics showed a few - all had the P next to the number and a couple had T14. I'm kinda thinking T is for the Tonawanda foundry since T was also used in the assembly stamping. I've no idea if other foundries were also making 454 blocks. The few small blocks I searched didn't use an F or V on the casting flange, just a number separate from the part number.
Casting info and date for same block:
3999289 P2.jpg3999289 date1.jpg
Different block, no casting date posted:
3999289 P3.jpg

Small blocks:
s-l1600.jpgs-l1600b.jpg

[Joe L.]

Re: LS4 Cylinder Block Casting Number

Yes, there is a "P" stamped on the block. "See attached picture I just took." There is a GM T12 and below that: 3999289 (vertically) and to the right of that block number, "P".

I am asking what the P stands for. Also, T12?

George Hunt
'73 LS4 / M21.
3rd Eddition 73-74 TM Team Member.

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George------


If your photo had been attached to your initial post I would have responded differently. Somehow, I got the idea that the block was absent a "T" casting mark anywhere.. Obviously, now, the block has the "T" which definitely indicates a Tonawanda casting. As others have indicated, the "12" following the "T" is the pattern number that the sand mold was created from.

All of the Corvette and passenger car big blocks I am familiar with have the term "PASS" embossed on the block to denote a passenger car block (i.e. short deck). Apparently, in later big blocks (or, perhaps, just ones with the 12 pattern number as there can be such minor variations from pattern-to-pattern), the "PASS" was replaced with just a "P". I was unaware of that; now I am. I just knew I came around here for some reason!