Improvement of Formula Student Racecar Performance with Variable Runner Length for the Intake System

This study focuses on achieving a lower overall lap time at SAE Formula Student competition through a modification to the standard intake system. The lower lap time is achieved by widening the range of engine RPM which produces torque higher than 90% of the maximum value and lowering the engine RPM corresponding to the maximum torque. An intake system with ‘variable runner length’ is introduced to the 2015 racecar of KMUTT team. The values of intake lengths are determined from the wave equation with the goal of producing over 90% of the maximum torque of the baseline configuration over a range of engine RPM. Computer simulations are performed to determine the pressure at engine entry at various runner lengths. Finally, a prototype variable runner length intake system with linear motor actuators is constructed and installed on the racecar. Chassis dynamometer tests are performed to determine the engine torque for 3,000 – 10,500 RPM at all interested runner lengths. A final variation of runner length with respect to RPM is constructed by combining the data from test results. The modified engine is able to deliver torque above 48.47 N-m (90% of maximum torque) over 4,746 – 7,368 RPM, which is 95% wider than the original power band of 5,784 – 7,127 RPM obtained with the constant runner length. A test run shows that the time taken by the same racecar to complete a 75m drag race is lowered by 0.30 seconds or 6.37%, and a computer simulation shows that the Autocross lap time can be lowered by 3 seconds or 4.11%.