The Effects of Intake Geometry on SI Engine Performance

Intake tuning is a relatively simple alternative to turbochargers and superchargers as a means of augmenting engine performance. Capitalizing on air flow harmonics at specific engine speeds, intake tuning forces more air into the engine cylinders, resulting in greater torque and power. Concepts such as Helmholtz Resonance Theory and Reflective Wave Theory help to describe the physical phenomena that contribute to intake tuning, but previous studies have generally found that computer models utilizing computational fluid dynamics (CFD) are needed to accurately predict performance effects. The current research involves testing various intake runner lengths and cross section geometries on a Honda CBR600 F4i gasoline engine typically used to power a Formula SAE car. Also, the effect of adding 180 degree bends to intake runners is evaluated. Results provide empirical verification of computer modeling and confirm the role of reflecting compression and expansion pressure waves as the primary mechanism of intake tuning. This research identifies short-length intake runners in the range of 0.25 to 0.45 meters as the optimum runner length for application in a Formula SAE car, both in terms of implementation feasibility and consistently high engine torque, power, and volumetric efficiency. Additionally, adding bends to intake runners may prove to be an acceptable means of packaging intake runners within small car frames.