Evaluation:

With the final manifold design fully developed, the team then evaluated its effectiveness in terms of improvement over the stock system. Of course, the best method of evaluation would be to construct a prototype and repeat the dynamometer test with the new manifold in place. Since time constraints did not allow such methods, the system was evaluated according to its expected performance.

From the results of the experiment, it was clear that the increase in VE due to the pulse effect of the primary pipe is between 10% and 15% at 7000 RPM. The magnitude of the boost at 5500 RPM is more difficult to project, but data published for similar systems suggests that one may expect up to a 10% increase in VE at the tuned speed of the Helmholtz resonator. For the evaluation, the team chose to make a best-case scenario approach.  Therefore, these values were accepted as the VE changes due to the pulse-ram effect.

The benefits of the new manifold in terms of flow resistance and fluid momentum loss were also considered. To obtain a flow analysis, both the stock and new systems were modeled using the ALGOR FEA package. In this analysis, a worst-case approach was employed, in that the flow was modeled at its highest possible rate, which would correspond to the maximum restriction and momentum loss. Two-dimensional models were constructed, taking a horizontal slice of the manifold at the maximum pipe widths. Appendix B contains a summary of the FEA modeling process. the figure below shows a model of the original plenum, for the charging of the outer cylinders (1 and 4) and the inner cylinders (2 and 3). Gas velocity profiles are shown at left, and pressure fields at right.  Note the unevenness of flow due to the asymmetrical layout of the plenum (velocity profile).   Also visible in the pressure fields are zones of turbulence and separation, characterized by higher pressures.  The air must undergo multiple 90° turns along its flow path, resulting in momentum loss. These are the flow restrictions that the team desired to reduce in the final design.

CFD model of original plenum

CFD model of final design

The image above shows a similar model of the final design’s plenum. Again, both velocity and pressure plots are shown, and both intake cases are considered.  Note the improved straightness of flow, resulting in less fluid momentum loss. In addition, the regions of restriction are reduced in comparison to the stock system. By examination of the models, the design team estimates an improvement in VE of about 5% due to the reduction of flow restrictions in the new plenum.

Once the relative performance increases had been noted, it was then possible to generate a projected output curve for the pulse-ram-equipped motorcycle. The graphs below show an overlay of this projection on the original dynamometer curves. A significant increase in both torque and power is projected over the target range.  The maximum improvement is apparent at 7000 RPM (+35%). Another output peak centers around the secondary boost point (5500 RPM), and both curves are shifted upward by about 25%.  This is due in part to the improvement in flow through the plenum (5%), but the greatest single improvement was apparently due to the switch to a high-flow filter from the previous oil-soaked foam model.

Final design Projected torque

Final design projected power