The art of creating great cylinder heads includes many different things, but a large portion of it comes from lots of time spent with a grinder in hand and in front of a flow bench, determining just how effective your changes are.

Yes, the most critical component is how the engine responds to the cylinder heads you either purchased or ported yourself and how the racecar performs on the track, but the last thing you want to do is race a set of cylinder heads if you have no idea how they will perform. And dyno testing every cylinder head, or port design, is prohibitively expensive.

That's why a flow bench is so important to the cylinder-head specialist. So far, it's the best way to quantify just how well a port in a cylinder head can flow air and fuel. Typically, cylinder-head specialists use a flow bench to measure how much air (measured in cubic feet per minute) will move through an area when a specific amount of vacuum is created. The strength of a vacuum is measured by how far it will pull water through a tube, and the common value for measuring cylinder heads is 28 inches of water. It isn't important to understand exactly how much vacuum that is; just that it's the standard. So if you see an ad or someone throwing out cylinder-head flow numbers that just don't seem right, check to see at how many inches of water they did their testing.

A flow bench will measure the overall flow through a port, but often, cylinder-head specialists want to know more than just a general flow number. For example, is the short turn of the intake port too sharp, killing flow? Or can the roof of the port be raised without killing velocity? When cylinder-head specialists want to know how air flows through a specific section of a port, they typically use a Pitot tube.

A Pitot tube is a small tube connected to a pressure measuring device that can tell you how much air is flowing past a specific point. This is a very useful tool that has been used for years by head porters because it allows them to look at very small areas of the intake and exhaust ports and determine where the strengths and weaknesses of the port are. After all, all areas of an intake and exhaust port do not flow air and fuel evenly, so a head porter is always looking to determine exactly where the weakest areas of his port designs are and make changes to strengthen them.

Although it's a valuable tool, the weakness of a Pitot tube is that in order to measure airflow, it has to be inserted into the airstream. And even if it is very small, it still displaces some area in the port. So no matter how you use it or try to minimize the problem, a Pitot tube is always interrupting the airflow in the very area you are trying to measure! For cylinder-head specialists, that drawback has been considered a necessary evil that you have to account for. Until now, that is.

Richard Touchette, a longtime engine builder and cylinder-head specialist, has invented a new device that allows anyone to precisely measure flow around either the intake or exhaust valve without impeding the path of that air.

Touchette, who also founded RTST to handle the manufacturing, calls his invention the "Pressure-Differential Valve," or P-D Valve for short, and its genius is in its simplicity. Touchette actually embeds his Pitot tube inside a mock valve so that it's completely hidden from the airflow. The readings with this setup are more "pure," because there's nothing in the way to obstruct airflow.

"Around 1995, I was doing a lot of research and development on race-engine cylinder heads with flow-bench test equipment," Touchette explains. "I was also using a Pitot tube to do port mapping to see how the pressure differential changed though different ports. But a Pitot tube placed in the flow path of a cylinder head produces flow obstructions which makes it hard to get the true numbers when you are trying to produce a pressure differential map of a port. It can be a bit frustrating.

"I began to experiment with ways to construct Pitot tubes that didn't obstruct the airflow and tried different designs to see how well you could use them to map pressure differentials within the port. From that, I developed the P-D Valve which, I believe, will aid people doing research and development on cylinder heads and port designs because, unlike a standard Pitot tube, it can give you a true map of how the air flows around the valve."

Along with the valve itself, Touchette's invention (which is so new the patent is still pending) includes the ability to control the depth of the valve in the combustion chamber and software that helps map your results so you can interpret your findings through graphics instead of staring at a bunch of numbers. Just about everything else needed is standard equipment on almost any flow bench.

The first step in using a P-D Valve is to determine exactly what cylinder head you will be testing. In order to get the best-possible numbers, you will need to use a P-D Valve sized exactly like the valve that will be running in the completed engine. Touchette says he plans to keep many of the most popular sizes in stock, and custom P-D Valves can be made for specific applications. If you like, you can even cut your own valve seat angles in the P-D Valve.

Once you have the correct valve, testing can begin. The P-D Valve has a hole (the correct term is a "pressure tap") in the seat area of the valve that extends all the way through the tip of the valve stem. To get your readings, all you have to do is connect a piece of tubing from the top of the P-D Valve's stem to a pressure gauge. In most instances, the flow bench will have provisions for connecting a Pitot tube to a built-in pressure gauge, and hooking up the P-D Valve is no different.

In order to get repeatable results, Touchette includes a slip collar with a set screw and a set of height standards. The standards allow you to set your valve height off of the seat in increments of 0.050-inch all the way up to 1 inch. Once your height is set, use the set screw to lock the valve in the slip collar and its height will be consistent during your test.

Because the P-D Valve has one pressure tap, it measures one specific area of the port. In order to get a complete look at the airflow all the way around the valve, you need to do a sweep at a particular valve height. To enable this, the P-D Valve's stem is cut with eight splines equally spaced along the length of the stem. These connect with a ball pin detent in the slip collar so you can click to the same eight spots time after time. The slip collar connects to the top of the cylinder head and stays in place during porting or other work to the head, so after you have made changes, you can use the P-D Valve and test in the same locations as before. It's this repeatability that allows a good cylinder-head man to pinpoint exactly where a port and combustion chamber need to be improved and make his changes.

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.

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.

 SOURCE RTST
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