C2 cylinder head casting no. question

[Ronald Phillips]

Greetings All,

I have a 1967 300 hp motor that I'm currently rebuilding. On one side of the block is a head with a 3890462 casting and a date of E57. On the other side is a 8917291 head with a date of E197. All of the information I've seen on the 291 casting suggests that it was used from 1968 forward, and that this motor should have 462 castings and only 462 castings, is this the case? The casting dates fit with the build of the motor, and the car.

This motor comes from a corvette that I bought 18 months ago, from the original owner, who kept all service records from the time of purchase on. In these records, there is nothing suggesting a cylinder head replacement. The motor has never been apart, according to these records, and has very little wear. Thanks in advance, and apologies in advance if this question has been asked before ( if it has, I sure couldn't find it).

All best,

- Ron

[jordan grant]

Re: C2 cylinder head casting no. question

I just recieved my first issue of "the corvette restorer"and read something about this very topic!.Page 30 addresses head castings and various # oddities that I'm sure would help.Mark Gorney ncrs#35760 wrote the article(I'll assume he wontmind as he put his name in the "restorer".He specifically refers to head casting 3890462 being mixed with 3782461!.Maybe your heads were matched at the factory as he alludes to in this article.Good Luck.Jordan

[Joe L.]

Re: C2 cylinder head casting no. question

Ron------

The GM #3917291 was used for late 1967 as well as 1968. A May, 1967 date on the head castings certainly qualifies as late 1967 and May, 1967 is, curiously, just about the time that the changeover from the '462' castings to the '291'castings occurred. Given the dates on your heads and what's known about the changeover, I have no doubt that both heads are original to the car.

The only easily discernable difference between the '462' head and the '291' head is that the '291' has a boss for the temperature sending unit. In the case of your head, this boss is likely not drilled and tapped. The Flint engine plant didn't really worry about having "matched sets" of cylinder heads if the heads, regardless of casting number, were functionally equivalent.

[Ronald Phillips]

C2 cylinder head casting no. question

Hi Joe,

Thanks for your quick response. Yes, the 291 head has the sending unit boss (undrilled) as you stated, and the 462 casting has it as well. The most striking difference between the two is that the 291 has rectangular openings in between the pushrod guide holes. These appear to be "as cast", with no secondary machining evident - some of the openings exhibit a lot of casting flash.

All best,

- Ron

[Joe L.]

Re: C2 cylinder head casting no. question

Ron----

If your '462' head casting has the temp sender boss, then it must be some sort of a "hybrid" casting, perhaps using mold components of both the '462' and '291' heads. Generally, '462' castings don't have the temp sender boss.