1972 LT-1 Cylinder Heads- Different Numbers

[Bob H.]

I have what is supposed to be the original engine which is an 014 block with a date of mid May. I was pleasantly surprised when taking off the right side valve cover to discover a 487X head with a date code 03/08/72. When I removed the right side cover, I found the head dated 04/17/72 but casting number of 3998993. While researching, I found someone with a late LT1 that said his original engine was the same as mine, different numbers. Can anyone shed some light on this?

[Ray K.]

Re: 1972 LT-1 Cylinder Heads- Different Numbers

Bob,

This does not answer your question as to why different cylinder heads but just a little more information. The Corvette Black Book does reference both casting numbers - #3973487 and also the #3998993 with the #993 having the notation "uu" which is defined as uncertain usage. Also odd is the #993 was supposedly only installed on 200HP engines.

Ray

[Bob H.]

Re: 1972 LT-1 Cylinder Heads- Different Numbers

I found an article about an "M" cast in the head and have now lost it about cylinder heads that were more or less used to identify a certain run of heads. Wish I could find the article again. This has an upside down W (M) 33 cast into it.

[Cecil L.]

Re: 1972 LT-1 Cylinder Heads- Different Numbers

MCode 1 .jpgMcodecastings.jpg

[Mark F.]

Re: 1972 LT-1 Cylinder Heads- Different Numbers

Thanks Cecil...very interesting !

So Bob, based on the letter Cecil just posted, your "M33" head was one of the two heads in the cope and drag molds for the "M33" and "M34" sample pair run.

Although they were cast together, by the time they went thru shakeout; machining; inspection; shipment to the engine plant; the "M34" head in the other half of the mold yours was cast in - after all the processes listed above - went into someone else's engine.

[Bob H.]

Re: 1972 LT-1 Cylinder Heads- Different Numbers

sure looks like it. Original engine was rebuilt in 2012at 78K miles

[Bob H.]

Re: 1972 LT-1 Cylinder Heads- Different Numbers

Just came across the post above from 2017 which sheds a bit more light on how this was possible. Willing to bet the 993 has 202 valves. Looking the engine build