Here's a shot of our test subject, the intake port (second chamber from left) of a Brodix
To test the new P-D Valve, we travelled to the shops of MBE Cylinder Heads & Manifolds where cylinder-head specialist Matt Bieneman set us up on his SuperFlow flow bench. For our test, we used a couple of Brodix aluminum heads for Chevrolet big-block engines. These heads are a hot ticket in Dirt Modified racing in the northeastern United States, and Bieneman had just completed a new port program that we thought would make for some interesting results.
For our test we only looked at the intake port and compared one stock port (and combustion chamber) to one that MBE had reworked. The Brodix head features 2.400-inch-diameter intake valves, and the seats were the same. Bieneman says the difficulty of working this otherwise-excellent head comes from the arrangement of the valves. On one of the center two cylinders, the intake valve placement forces the intake charge to change direction from the intake manifold runner to the intake port. This causes all the airflow to want to go to one side of the valve. Getting even flow all the way around the valve is impossible, but improving flow all the way around is the key to good performance.
This blueprint-style drawing gives a good view of how the Pressure Differential Valve fits
Using this head, Touchette was able to quickly make a map of air-flow around the intake valve in 10 different stages of valve lift (0.050- to 1.00-inch off of the seat). The process is relatively simple: The operator locates the valve at the correct height for the test, sets the valve in the first detent position, turns on the flow bench, and gets the pressure reading. Next, he inputs that number into the program, and the software uses the pressure reading along with the vacuum pressure and converts that information into the amount of airflow (in cubic feet per minute) as well as port velocity. After the first reading is taken, the operator can spin the valve in the detent to the other seven positions to create a complete, 360-degree map of how the air behaves all the way around the valve.
The setup we used was a preproduction unit, and Touchette says plans are in the works to upgrade the software by the time you read this, so that it can produce three-dimensional maps of airflow that combines both 360-degree sweeps and valve lift at several different levels. Still, we were able to compare sweeps at different valve lifts to see how airflow changed as the valve extended farther into the combustion chamber. Bieneman's port for this big-block race head was designed to maximize high-lift flow, and that's exactly what it did. It was also interesting to see how the highest-flow areas moved around the valve as lift increased. Another interesting observation that is quite evident with the P-D Valve is how much the valve stem disrupts airflow. Those narrowed valve stems may be expensive, but there's definitely something to them.
The P-D Valve is an advancement of the technology available to engine builders and cylinder-head specialists that should help improve engine designs in the years to come. It should also help everyday racers like us determine which cylinder-head designs are really better than others more quickly and economically. It's just one more tool available to you to help make your racing program more successful.
Here's a printout the software provides. Please note that this was still a preproduction version of the software and may be different from the final build. Still, the basic premise will not change. The operator takes the readings from the eight positions as the P-D Valve spins 360 degrees and inputs them in the "Pressure" column in the table. The software takes this information and converts it into airflow (measured in cfm) and velocity. It also creates a color-coded chart to allow you to easily see how flow varies around the port. This printout is from our test of MBE's reworked cylinder for the Brodix head with the valve at 0.500-inch inside the port. Notice how the highest flow numbers are at the 9 o'clock position in the port and the valvestem blocks flow at the 12 o'clock position. Comparing these charts can help you quickly and easily determine if changes you have made to a port or combustion chamber are an improvement over an earlier design.