dano nailed it! The big dif between the 426 Hemi and the ball stud Hemi was the swirl fill of the cylinders, as Tom Hoover stated. It's very possible that Ford got wind of Chrysler's research with the Hemi and used that info for the Boss motor. It's not like they built a whole new motor. Chrysler had already been playing with different heads, including an overhead cam Hemi. As was typical, NASCAR kept changing the rules until the Hemi's were no longer competitive. NHRA did the same thing.
Take a look at the new street Hemi's or the NHRA pro stock Hemi and you will see this high swirl port and combustion chamber in full swing. The pro stock Hemi actually looks very similair to the A279. The new street Hemi does it by making the intake port curved coming into the cylinder, instead of twisting the valves (they are still in line left to right).
From PHR:
Flow Capability
We can see that Chrysler's engineers were targeting the best two-valve head possible. There are two important questions that need to be asked here: How well did they succeed for the head in stock form and, since no aftermarket heads are available, what is its porting potential? The graph, Fig 3, gives the answers here and you are going to like them. First, the intake port. The stock port with its 2-inch valve flowed a whopping 270 cfm at only .600-inch lift. It hit the peak flow figures, which are produced at .700-inch lift on a stock LS6, at only about 375 thousandths lift. This is good news but there is a lot more. Peak figures are not the whole story. Good mid-range figures are also important. The new Hemi did extremely well here. At 250 thousandths lift, the stock head was nearer a $10,000 Winston (Nextel) Cup head than it was to even a good modified parallel-valve head.
A check on the intake port velocity (Fig 4) showed the intake to be a super high-speed port with valve-to-port areas very similar to what is seen in Formula One. Velocity probing showed 90 percent of the port flows at a velocity greater than 90 percent of maximum. This is far better than a typical 23-degree performance head for a small-block Chevy or, for that matter, the LS6.
The exhaust port showed the same high-function trend by hitting 161 cfm at 600 thousandths lift through its 1.55-inch valve. It also had a far better than average port velocity and velocity distribution (Fig 5).
We spent a day and a half on the flow bench in an effort to find out what this head does or does not like in the way of port mods. We are sure there is much still to come, especially with some bigger valves, but we did find what it took to produce, at 600 thousandths lift, some 302 cfm on the intake and 195 cfm on the exhaust. As the nearby photos show the work to achieve this proved simple. In essence, the porting involves little more than just tidying up what Chrysler's engineers provided in the first place (great job guys).
