Now, study Figure 5. This is a visualization of how you can "map" a passage, section by section. Using the velocity probe, record readings at each "corner" of a given section, along with the highest pressure read elsewhere in the port; e.g., ideally at its center. Each of these readings is taken in the plane of each section. By assembling the data from all sections in the passage, you can determine the pressure distribution profiles for the entire path, entry to exit. Although there will always be compromises, the goal is to create a passage (including directional changes) that trends the center of pressure distribution toward the geometric center of the passage. This is critically important in wet-flow conditions and significantly important during dry flow. Remember, the lower the dynamic pressure, the lower the flow activity and the greater the possibility for turbulence (in dry flow) and air/fuel separation (during wet flow).

Using the "boundary layer" probe (open end facing atmospheric pressure), you can navigate these same sections as were examined with the velocity probe. In this instance, you'll be looking for manometric gauge deflections opposite to what you saw using the velocity probe. When you find them, it's an indication the working fluid (air or exhaust gas) has separated from the passage walls, creating a lower than atmospheric condition that hampers dry-flow efficiency and can lead to air/fuel separation during wet flow. You'll also discover that at the point of greatest velocity (within a given section plane), the boundary layer probe will not cause the manometer to move. This is because both sides of the manometer (at this point) are experiencing atmospheric pressure. It's a quick way to also map maximum velocity pressure in a passage (section to section).

Now, you may decide all this isn't very scientific. And, by some contemporary standards, it's not. There are far more accurate and expensive ways. But for our purposes, you'll quickly discover that what you're attempting to do is compare readings on a test-to-test basis, so units of measurement can be grid-count, portions of an inch or virtually any linear unit of manometer gauge information. Using this rather crude system, you can make serious progress creating (or evaluating) changes to achieve stable, uniform, low turbulence port flow.

At the end of the day, you'd like to minimize manometer deflection, as measured by the boundary layer probe, and equalize section pressure distribution with an emphasis on trending the center of pressure toward the center of the section, using the velocity probe. You can also use this method to evaluate parts known to work well, in the sense you'll develop a better understanding why. "Getting there" is one thing. "Knowing how you did" is another matter, and you need to understand them both.