OK.  This is great info.  I was also wondering if ALL '57 G code heads were physically the same.  Some were cast at Dearborn others at Cleveland.  Specifically, was there anything special about the 312 G code heads that were on an E-Bird?  I ask since the G code heads could be found on trucks, Mercs, Fords, and T-Birds. A friend insists that the small letter G code head with (intake side cast) are specific to the T-Bird.  Is that correct?  Also, did T-Birds only use G code heads cast at the Cleveland foundry?

A further note on the early small letter "G" heads. Our senior moderator, Ted E. says they should not be milled more than 0.025"  due to the thinner decks & no posts.


Paul

62bigwindow.  There's three (3) species of ECZ-G cylinder heads that were used in car production year 1957 on y-block 272, 292, and 312 engines.  The large letter ECZ-G heads were cast in a different foundry than the heads with the small letter ECZ-G markings. 

Early '57 production year large letter G heads were un-posted until May of the '57 model year.  Commencing sometime in May 1957 (this is based upon casting date numbers) the large letter heads began being cast with 'posts' added to provide additional strength in the deck area.  Outwardly, to my knowledge, the un-posted and later posted large letter G heads cannot be told apart unless you look at the date codes under the valve covers.

None of the small letter G heads had 'posts' regardless of when they were produced during the '57 model year.  Again, these were produced at a different iron foundry than the large letter G heads.  What's always been amazing to me is that while the large G and the small letter G heads outwardly appear to be identical except for the casting ID, (AND the combustion chambers also appear to be identical, too) ...the small letter G heads were produced using different sand cores for creating the intake ports and the exhaust ports than what were used for making the large G heads.

What has registered with me when I've compared the two series of heads (large letter G and small letter G) is that the intake port flow into the underside of the intake valve appears to be 'better' shaped on the small G heads than on the large G heads.  Conversely, where the exhaust port exits the cylinder head to meet the exhaust manifold, the opening size is significantly smaller on the small G heads than the opening on the big G heads.

Personally, in doing porting work, for shaping purposes, I have historically preferred the small G heads even though they are not posted.
In the archives of our Forum are one member's step-by-step depiction and pictures of how un-posted heads can be appropriately posted.

Interestingly, ALL '57 'Birds were produced with 292 or 312 engines (except the supercharged 312s) that had large letter ECZ-G heads.  1958 Mercurys that were equipped with312 engines also had large letter ECZ-G cylinder heads that should have posted cylinder heads because of their production date.

Sooo... there are posted and un-posted large letter G cylinder heads and un-posted only small letter G cylinder heads.

Hope this helps.


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

This is more of a question than a statement. Are not there posted and unposted g heads? Would that be an easier way to distinguish between the two?

Durham Missouri

BamaBob.  Click the link below and read through the entries.  It should provide you with pictures, point out the orientation difference of the letters on the two different series of G heads, and give you the dimensions of the letters for the two different G series also.

http://forums.y-blocksforever.com/FindPost113734.aspx

Hope this helps.  


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Just for identification purposes, the location of the letters is an easy check.  The big letter, early style have the casting numbers near the exhaust ports while the small letter are a little harder to find.  On Mummert's website, he has pictures of where numbers are located at the top of the head identification page. The C pic is like big letter and the 113 pic is like small number.

Don

Can anyone tell me how to tell the difference between large letter heads and small letter heads without having the two side by side to actually compare them? Or, better yet, does anyone have pictures of the two that could post them here? Thanks to all for the excellent information posted here!