C3 head casting Number

[Paul K.]

I can not find this head number in my book. Can some tell me what it is from?
casting 399 492, there is no number between the 9 and 4, dated A11 1

Paul Klemetson

[Mark F.]

Re: C3 head casting Number

I can not find this head number in my book. Can some tell me what it is from? casting 399 492, there is no number between the 9 and 4, dated A11 1 Paul Klemetson

Paul,

Check out post #4 by Joe Lucia in the link provided below. He knows more about GM numbers than anyone I know...

Here's an excerpt of what he said...but you should read the entire string...

"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..." (this post was back in 2000).

I've seen other references to the missing # between the 9 and 4

https://www.forums.ncrs.org/showthread.php?5268-1970-LT-1-head-(-)-need-help-with-numbers&highlight=3991492

[Paul K.]

Re: C3 head casting Number

Thanks for the info,
Paul Klemetson

[Bill B.]

Re: C3 head casting Number

Hi Paul,

I have several of these unique over-the parts-counter GM heads (a pair installed on my engine). They were available in both straight plug and angle plug versions. (I have the latter). They are 64 cc, and back in the day, were sought after state-of-the-art for a GM offered cast iron "double hump" head for the SBC. I recall rumors back then indicated an approx. 10 HP increase for just bolting them on. I believe the fine print with that claim might have been associated with the angle plug version when used with a high dome piston, as the spark plug would have been situated in better position to provide better flame propagation during the initial ignition of the air/fuel charge in the "squish" area of the combustion chamber. (Duke W. can provide a better technical explanation of why this is).

In my opinion, these "492" head castings are collector's items, as finding a set of un-molested units are getting slimmer as the years go by.

[Terry M.]

Re: C3 head casting Number

I remember a set of those setting on the paarts counter in a long gone Chevroelt dealer -- angle plug. Complete head; valves, springs et al. I almost bought a set for my LT1, but it was more money than I had at the moment given insurance and monthly payments.