1970 LT-1 head (?), need help with numbers

[Brett A Wheeler]

While going over the non-original motor in my '69 convertible to see what was there, I came across a casting number on the driver's side head that reads 3991492. There are also the codes "E2A1" and "GM 46" cast into the head. A source that I refernced indicated that the head could be a 1970 LT-1 head or an over the counter Camel Hump head. If anyone can decipher the latter two and/or tell me whether or not I have an LT-1 head, it would be most appreciated.

Thanx in advance, Brett NCRS #32566

[Joe L.]

Re: 1970 LT-1 head (?), need help with numbers

Bret-----

GM casting #3991492 was not originally used on any Corvette engine. I will have to check other references later to tell you what it was used on. The "GM 46" is the mold number that was used to cast the head. It is cast into the heads so that if there is a service problem with the heads, they might be able to track the problem back to a particular mold it was "born from".

The "E2A1" looks sort of like a date code, although the "A" part of it doesn't work, and you may be misreading that character. The "E" would denote the month of May and the "1" most likely denotes 1971, although it could also denote 1981 or 1991 if the 3991492 cylinder head was still in production during those years. The numbers between the "E" and the "1" represent the day of the month.

Just because this cylinder head was not originally used on a Corvette does not mean that it is significantly different than Corvette heads. It may be a SERVICE replacement for a Corvette application or it may be an equivalent head which was originally used for some other application, but not Corvettes. I'll be able to tell you more later.

[Jephrey S.]

Re: 1970 LT-1 head (?), need help with numbers

Brett, My driver's side 70 LT1 head reads 3927186 L29 (spaqced far apart, no 4th number, but maybe no 3rd number) and GM51. Jeph

[Joe L.]

More Information

Brett-----

As it turns out GM casting #3991492 is a SERVICE-only cylinder head that was in production since about 1970 and continuing to this very day. It was originally sold under GM PART #3987376 and currently is known as GM #12480092 and it was probably known as many other part numbers along the way. This casting was used for both 2.02/1.60 and the 1.94/1.50 valve sizes but, when sold under GM #3987376 and the current GM #12480092 it has the 2.02/1.60 valve size and is the SERVICE replacement cylinder head for 64-68 with special hi-performance 327 and 69-70 with L-46 or LT-1.

Over the years this cylinder head casting has been used for both angled and straight plug finished cylinder heads and using both gasketed as well as tapered seat spark plugs. The current version features straight spark plugs.

Most versions of this cylinder head casting have screw-in studs and guide plates. The combustion chamber volume is 64 cc, nominal. These heads DO NOT have and never have had induction hardened exhaust valve seats.

So, the bottom line here is that these heads, although never ORIGINALLY used on a Corvette or other production car, are essentially the same and are the SERVICE replacement for 1970 Corvettes with LT-1 engine and, of course, the other Corvettes that I mentioned.

Most of these heads were made at the Flint V-8 engine plant but I believe that as of several years ago the tooling used to produce them took up residence at the GM Powertrain Plant in Toluca, Mexico. If it didn't then, I expect that it has by now.