Reply to "Edelbrock Intake. Modify or not Modify?"

What has already been written is true, Edelbrock specified using the manifold "as-is", do not grind the manifold larger to match the 4V intake port inlet. Although the 4V intake port inlet has a cross-sectional area greater than 4 square inches, the ports "average" cross-sectional area is only 2.9 square inches. The opening of the port was flared open to operate with "wide open induction system" style intake manifolds, which was the trend in racing manifolds in the late 1960s. The 4V intake port entrance is about 2-1/2" tall, yet the runners in the factory intake manifolds (and the Edelbrock manifold too) are not nearly that tall, they are closer to 2" tall. So the factory intake manifolds flare open to match the height of the 4V intake port entrance. If you can visualize this, the gas flow in the factory induction system starts in a runner with a cross sectional area of about 3 square inches, then it expands to a cross sectional area over 4 square inches, then past the intake port entrance it returns to a cross-sectional area closer to 3" again. This is not ideal. Basically, Edelbrock designed the runners of their Performer intake manifold as if the 4V intake port did not flare open at the inlet. One way to make the cross sectional area more consistent would be to fill the intake port inlet to match the Edelbrock manifold. Filling the inlet of the intake port about 1/8" on the left side, and about 1/2" on the floor, gives the intake port a more consistent cross-sectional area (the average cross-sectional area is reduced to about 2.7 square inches) and makes the port smoother, eliminating the bumps and ramps built into the ports entrance. The other way to achieve a more consistent cross-sectional area is to use the Blue Thunder manifold, which has full height runners that compliment the opening of the 4V intake port; the Blue Thunder manifold was designed to be a "wide open induction system" manifold, which is why it was originally available with a carburetor mounting pad designed for 1050 cfm Holley dominator carburetors. It works very well with the iron 4V heads.

The small carburetor you've chosen will limit the volumetric efficiency of your Pantera's motor, it makes no sense at all to cut down the plenum to improve high rpm power, but at the same time restrict the motor with a 670 cfm carburetor. The size of carburetor you selected indicates to me you were concerned about low rpm drivability, if that's the case a full height plenum divider will compliment that choice. As far as I'm concerned, a full height plenum divider compliments the reasoning for choosing a dual plane intake manifold in the first place ... optimized performance at the rpm most often used when driving on public roads.

One way to gain horsepower at all rpm (about 25 to 30 horsepower on top) is to block-off the exhaust heat passage built into the intake manifold, if the winter weather where you live will allow this.

-G