Restricting the airflow to the engine is a convenient, and therefore common, method of regulating engine performance in many forms of motor sport. Formula SAE, and its European counterpart Formula Student, impose such restrictions on engine configuration. The capacity of the engines must not exceed 610cc but, more specifically to this study, the intake system must be fitted with a 20mm diameter restrictor through which all the air must pass.
There are, however, a number of geometrical parameters which can be changed to maximise the performance of the restricted engine. In this study, the effects of modifying the restrictor design, intake runner length, intake camshaft profile, exhaust geometry, and silencer design were measured using a transient dynamometer. These tests were performed on a 600cc four-stroke, four-cylinder Yamaha YZF R6 engine. For each configuration examined, the ignition timing and fuel maps of the DTA engine management system were optimised using torque and emissions readings.
The optimum engine configuration produced an increase in peak power of 12kW (16hp), 23.5% greater than the standard engine in restricted format. In addition, the torque curve was significantly improved with 90% of the peak engine torque available over the useful speed range of 6,000 - 12,000rpm. This provides progressive torque delivery and makes the engine much more suitable for FSAE and Formula Student applications.