VLX 600 Intake Manifold

I am in the process of converting a Honda VLX 600 motorcycle from its original carbureted fuel system to electronic fuel injection. One of the most challenging components to design and manufacture is the new intake manifold. Early in my research I discovered that the geometry of the manifold can be tuned so that it actually boosts the engine’s performance at certain rpm ranges. This effect arises from two related acoustic phenomena: quarter-wave or “organ-pipe” tuning, and Helmholtz resonance. I am designing the manifold to take advantage of both of these to enhance performance at a specific rpm band.

Because this is my first serious experience in designing a fluid system, I have spent a great deal of time gathering technical sources, textbooks, and papers on acoustic wave tuning and intake manifold dynamics until I felt confident that the geometry I am designing will achieve the desired effects. The runners will be manufactured as a combination of welded mandrel-bent stainless-steel tubing and a 3d printed plenum. For the runner inlets I have chosen a bell-mouth geometry with simple radius profile, as this shape balances favorable impedance for wave-tuning effects and also improves the discharge coefficient and volumetric efficiency of the runners.

At the same time I am working to ensure that the design is practical to manufacture, I am learning to use Ansys Fluent so that I can verify that the mass-flow distribution between the front and rear cylinders is as even as possible. To establish a baseline and help validate the simulations, I designed and built a custom Arduino-based data-acquisition system that uses a differential-pressure sensor together with an inexpensive inductive tachometer. This setup lets me measure the differential pressure across the current intake system versus engine rpm at wide-open throttle. These measurements give me a picture of how the stock manifold behaves and will serve as reference data for comparing the new design once it is manufactured and installed.