Dart designed its bench to simulate a Pro Stock-style air/fuel ratio of 13.7:1. According to Dart's cylinder-head specialist, Tony McAfee, once the bench was operating, Dart directed its efforts toward port changes that would increase fuel flow without sacrificing airflow. The other half of Dart's wet-flow R&D concentrated on port changes that would introduce the fuel into the cylinder in the most homogeneous fashion possible. In other words, McAfee and his team worked on moving as much fuel as possible (while maintaining a constant air/fuel ratio), yet working to mix the fuel with the air as evenly as possible. This is much easier to describe than it is to achieve.
Dart's first attempt at wet-flow development began with a redesign of the original Iron Eagle castings. "What's interesting is that often you won't see a big difference in airflow on a dry-flow bench between the Iron Eagles and the new Platinum heads," McAfee said. "The difference is all in the wet flow." Dart is now taking the next step of completely redesigning its line of Pro 1 small-block Chevy aluminum heads that will be sold under the Speed Flow Technology line. While much of what the Dart team has learned about wet flow with the Platinum line will be incorporated into these heads, there's bound to be some new stuff included as well, especially when it comes to combustion-chamber shape.
Our testing of both heads on a dry SuperFlow 600 bench proved out McAfee's statement, since the comparison of the intake airflow numbers between the older Iron Eagles and the wet-flow-developed Platinum series of iron Dart heads reveals virtually no change in the numbers.
New versus Old
The photos of the comparison of the Platinum heads to the Iron Eagles point to some interesting differences. With the intake valves removed, the vanes in the intake port are the most obvious. But more subtle changes include moving the spark plug in the Platinum head much closer to the center of the combustion chamber. Ideally, the spark plug in any engine should be placed in the geometric center of the cylinder. With Hemi engines, this is easy, but with Wedge-style engines, it's much more difficult. Placing the spark plugs closer to the center should have the effect of reducing the amount of ignition lead the engine requires.
Also notice how the combustion-chamber wall on the far side from the chamber has been laid back. This tends to coincide or line up with the long side of the port where a majority of the air and fuel move past the intake valve and into the cylinder. Angling the chamber wall away from the intake valve creates that heart-style chamber shape, but the reason is to allow the air and fuel to exit the intake valve with as little shrouding as possible.
Wet-Flow Testing
Much of what constitutes wet-flow development is a mysterious blend of objective test numbers and a voodoo-like subjective interpretation of fuel patterns in the cylinder. It's like some kind of weird combination of internal combustion automotive research done with black lights and tarot cards. As you can see by the comparison of the photos of the Iron Eagle and Platinum intake ports, there are subtle differences in the flow patterns. Keep in mind that our photos are taken as extended time exposures of around eight seconds. This was the only way we were able to capture what is a very dynamic situation in very low light conditions.
Note how the Dart development team moved the spark plug in the Platinum chamber (below) more toward the center of the combustion chamber compared with the Iron Eagle chamber (above)