How to Pursue Engine Designs for More Power

Last Month, We Explored Some Basics for Flow-path De- Sign and a Why Certain Shapes Work Better

- Jim McFarland

When we closed out last month’s discussion, we’d just mentioned what is commonly known as a D-shaped flow passage. The shape was suggested as an improvement from circular crossection passages on because it provided a wider “short path” during a change in flow direction. Whether shaped to enhance dry flow (particularly on the exhaust side of the combustion space) or wet flow on the intake side, this configuration tends to equalize flow pressure across the floor of the turn and favorably effect boundary layer control.

As you will note in the accompany illustration of a D-shaped port, there is a more uniform distribution of flow pressure pretty much across the port floor. This tends to reduce resistance to flow and improve not only quality but quantity of flow. And in this context, you will also see how the pressure distribution bullet is more favorable to flow efficiency throughout the turn from horizontal to almost vertical, in this example. We’ll re-visit this shape when we discuss flow velocity probes a bit later.