The goal was to show flow improvement over even a well-ported production head, allowing for strong power production out of the box in a street/strip application. When we got wind of the news that the early production prototypes were just finish-machined at the Edelbrock R&D lab, we headed out to have a look.
Starting at the combustion chamber, the familiar fully-open design of the '68-and-later production head was set aside in favor of the more efficient closed quench area-similar to the highly sought-after 915 production heads. With the correct piston clearance, the quench pad, along with a small quench area on the spark-plug side, induces turbulence to the mixture as the piston approaches TDC. The result, at least in theory, is a better burn, less tendency towards detonation, less total spark-advance requirement, and less exhaust-gas dilution of the mixture from the dead space in the production open head. The bottom line should be more power.
Another subtle change is in the spark plug location, with the more common 31/44-inch reach reduced hex rather than the production 11/42-inch. Besides having a more favorable position deeper in the chamber, the plug is angled slightly (15 degrees) towards the exhaust valve, as is the practice in most modern wedge cylinder-head designs. We like the chamber.
Filling out the chamber are a set of 2.14-inch intake, 1.81-inch exhaust valves in 21 4N stainless steel, complete with wear-reducing flash-chromed stems. The valves have an 111/432-inch stem, smaller in diameter than the production 31/48-inch, which removes material from the flowpath while reducing valve weight. The valves ride in premium heavy-wall manganese-bronze guides, which are highly wear- and seize-resistant. The top of the guide is machined to receive a small-diameter, positive-type valve seal. The seal type, in conjunction with Edelbrock machining on the spring seats, allows for the installation of dual springs without additional machining and accommodates very high lift. The heads come with a stout single spring, delivering 120-pounds seat load at the as-delivered installed height of 1.880 inches, and are able to handle up to .600-inch lift. The valves seat on ductile iron valve-seat inserts pressed into the head. The valve and seat combo has proven compatible with unleaded fuels in extended street use in other applications.
The intake and exhaust ports are in the conventional location, allowing for the retention of the stock manifolding, both on the way into and out of the heads. Though the port size is not significantly altered from production heads, the port shape is highly developed for efficient flow. The intake port widens significantly beyond the pushrod pinch, and extends to the valve via a nicely formed and finished port bowl and shortside radius. The huge, obtrusive guideboss of the production iron heads is gone. On the exhaust side, the bowl area resembles a radically ported production head, again with the flowpath lacking the production head's large guideboss, which encumbers flow. From the bowl, it's a short direct path out of the head.
Like Edelbrock's small-block Chrysler head, the big-block version does not carry an exhaust crossover-an item that has no place on a performance aluminum head. We also noted that the lower edge of the intake port face is filled in, rather than the cut-back style of the production heads. This allows the option of using a separate breast plate or valley cover, and individual composition gaskets at the manifold face. The stock one-piece valley pan/intake gasket can therefore be eliminated.