What you're striving to accomplish is a pressure distribution pattern that shows flow rates along the short-side of the turn to be as equal as possible to the long-side. Again, to the working fluid, this presents an environment where a pressure differential (change in flow direction) has not been experienced . . . or at least the negative effects are minimized. As in virtually any parts design or modification process, there are unavoidable compromises. The idea is to accept the fewest number of them that have any impact on a project's outcome.

A Few Concluding Thoughts If you persevered through this entire story, it's likely that you're wondering how you can apply what's been discussed. Having eaten my share of cast-iron dust while grinding on ports and heads, washing aluminum shavings out of my hair, and using eye drops to excess, I can tell you the foregoing is good information. Smokey once told me to try talking to CT readers as if they were sitting across the table from you, nursing a cold cup of coffee, and trying to learn from what you've learned. The material you've just read can be applied to your weekly racing engine. It's up to you to find out how well.

A "saturday night" approach to port flow mappingConsidering the large number of flow benches owned or accessible to weekly circle track racers, the following information is intended as an introduction to pressure distribution mapping in flow passages. Whether you are examining a wet- or dry-flow system (particularly if you're not using a wet-flow bench), the suggestions and illustrations provided are intended to get you off dead-center in these types of studies.

Essentially, you'll want to either build a "system" of three water manometers or one to which you can interchangeably attach two different types of probes. For the sake of simplicity, we'll call one of these a "velocity" probe and the other a "boundary layer" probe. As is typically the case with measuring devices or test equipment, each has benefits and limitations. From experience, you can expect the former outweighs the latter for these two methods.

You can build the probes in a variety of ways. One proven method uses malleable steel tubing of about 0.040-inch o.d. and 0.015/0.020-inch i.d. These can be attached to flexible plastic tubing connected to the manometer(s), the other ends of which are vented to atmospheric pressure. A suitable manometer(s) can be constructed with lengths of hard plastic tubing connected by flexible tubing that forms the U-bends and filled with colored water. The manometer(s) can be mounted on a plywood backboard on which some form of "grid" or "scale" has been placed so that you can record numerical differences in manometric readings.

Figure 4 is provided to indicate the types of manometer readings you can expect from the use of a velocity and boundary layer probe. Manometer No. 1 depicts fluid deflection direction when the boundary layer probe senses pressure less than atmospheric, as in the case of layer separation from the passage surface or (in other instances) turbulent or unstable flow. Manometer No. 2 is what you should see when there is no turbulence and/or when the probe only sees atmospheric pressure (as positioned in the figure). It will also appear this way at or near areas of high and stable port-flow velocity. Manometer No. 3 shows gauge deflection direction when using the velocity probe, higher readings being a function of increased flow rate.