Junk 842 Aluminum Heads

[VintageMusclecar]

Eric;

I don't know of any reliable way to ID an open chamber head from a closed chamber just by external inspection.

As far as the "open chamber" 842's, many were converted from closed chamber into "open chamber" back in the day by relieving the plug side of the chamber wall. Old-school racers trick trying to improve flow & flame travel before true open chamber heads were readily available. I've seen many closed chamber heads with this modification, even some cast iron ones. Somewhat risky mod though, as the chamber wall by the plug isn't that thick. You can only safely get about 1/2 way to an "open" chamber before the chamber wall starts to get too thin. Still helped flow & flame travel somewhat, at the expense of some compression & quench area.

Eric

[KevinCav]

Hi Guy's,
The way I have always identified the 842/074 aluminum heads is very simple and it is virtually foolproof. I have used this method for many years, it only takes a few seconds, and can be done easily without having to remove a valve cover.
The first thing I look for when I see aluminum heads on a BBC is to look at the end of the head for a core plug. A core plug on an aluminum head is a sure sign that it is an 842 head. They can be at one end of the head or both ends of the head. Late cast 842's (after about May 1st, 1969) don't have any core plugs in them, so you have to look closer at the head. I have never seen an 074 aluminum head with a core plug in it.
The second thing I look at is the Winters snowflake on the most easily viewed exhaust port. This is a dead give away as to an 842/074 head. On the 074 head the snowflake sits flat on the top of the exhaust port where the manifold/header flange will bolt up, and the height from the top of the exhaust port casting (where the snowflake is cast) to the edge of the where the valve cover gasket sits on the head is approx. 3/4 in. The 842 head is very different in this area and can be detected easily once you have seen a few of them. On the 842 head the spot where the Winters snowflake is cast is slanted up toward the edge where the valve cover gasket sits on the head. The height in this area of the 842 head is only 1/2 in. compared to the 3/4 in. on the 074 head.
These differences in the heads might sound hard to distinguish, especially in a crowded engine compartment, but when you look at a couple of sets of these heads you'll get pretty good at identifying them.