Although flow for an out-of-the-box head proved to be good, the Performers' real strong point proved to be its high swirl. Most other 5.0 heads suffer the same problem as the stock heads in that they lack sufficient swirl to maximize low-speed output. Because the swirl really takes off at higher lift, it is best to use, as we did, a valvetrain that can utilize this.
Cylinder Heads
The choice of heads for our project engine was not something that came about simply by hunting through catalogs. The UNC Charlotte flow bench was put to good use, and the results of many (but not all) of the popularly used heads were compared. One factor that played a strong role was the out-of-the-box flow-bench performance in relation to price. Here, the Edelbrock Performer RPM heads scored well. Not only did they closely replicate the flow figures of our smaller valved but ported Windsor Jr. Lites from World, but they also delivered some of the highest swirl numbers of any 20-degree Ford head. All these assets made them look good for our purposes.
A check with a few well-known engine builders who have great experience with a wide variety of heads sealed the deal, and a set was duly obtained from Edelbrock. The fact that the heads have high swirl means that better low-speed output is likely. This in turn allows a slightly larger cam to be used without the low-speed output becoming unacceptably low for the street. In practice, we found we could use a 280-degree-seat duration cam and still come up with a better low-speed output than an otherwise stock engine with a much smaller cam.
The Performer RPM heads from Edelbrock feature intake ports accurately located in the stock position so as to best facilitate port alignment. | 
Apart from good airflow characteristics, the Edelbrock heads also featured quality hardware in the form of good studs, guideplates, valves, and stem seals. Of great importance, though, was the use of a good spring and damper combination. These delivered a seat force of 90 pounds and 240 pounds at 0.500 lift. With it's 300 lb/inch rate, the over-the-nose force with our 0.575 lift valvetrain was 262 pounds | 
Edelbrock made the best of the stock port location by paying close attention to port form to maximize flow. These heads have enough flow to make good use of a nitrous kit. |
Other than the 2.02/1.60 valve combination, part of the good flow from Edelbrock's Performer RPM heads is due to the hand-blended bowl work. | 
Since the high-speed characteristics were an unknown until test time, the lash was done the conventional half-turn into the lifter travel. | 
The Edelbrock heads are port matched at the manifold face. To get the best manifold alignment, be sure to pull it down square and progressively. |