Steady-State Intake Flow in a High-Performance V-Twin Engine

The design of intake ports for high-performance internal combustion engines has traditionally relied on steady-state flow benches and prototype core boxes. In this study, Computational Fluid Dynamics (CFD) methods were employed to gain further insight into the characteristics of a high-performance motorcycle engine. In this particular engine configuration, the throttle is located in very close proximity to the intake port, and the effects of throttle position on the intake flow characteristics were examined. This study shows that steady-state CFD analysis can be used in combination with traditional flow optimization techniques to provide further insight for cylinder head development. The intake flow behavior in this engine was found to vary considerably as a function of valve lift and throttle position. It was found that at low valve lifts the intake flow is relatively uniform around the periphery of the intake port, but at high valve lifts the flow into the cylinder is biased towards the top of the intake port. This results in a tendency to promote tumble at high valve lifts, but not at low valve lifts. Small throttle opening angles were found to magnify the flow biasing effect at high valve lifts.