Abstract-Header is a component inside an exhaust system which delivers the exhaust gas flow produced by engine combustion process. UGM's FSAE car Bimasakti, which took part in a racing competition, needs components with excellent performance including the header component. The present study is aimed at obtaining the geometry of the header exhaust system that can optimize the power and torque of the engine KTM 450 SX-F while still complying with the Student Formula SAE competition's regulations. This research used an engine and one-dimensional gas dynamics simulation software known as the Ricardo WAVE. This software was used to simulate the powertrain system model of the 5th generation Bimasakti. From the initial model, changes towards the header geometry with variations in diameters and pipe lengths were conducted. After the best design has been obtained, developments towards at the above-mentioned design with additions of expansion chamber, stepped pipe, and diffuser shapes were then conducted. The obtained results showed that larger diameter of header can produce the better power and torque value at both low and high RPMs, whereas smaller diameter size would produce a better power and torque value at medium RPM. The effect of the use of longer header length can produce a better power and torque value at medium RPM, while shorter length would produce a better power and torque value at high RPM. Also, it is obtained that the addition of expansion chamber shape will reduce the engine's power and torque, while the addition of stepped pipe and diffuser shapes will increase the power and torque value at high RPM.Keyword-Header, Exhaust System, Ricardo WAVE, FSAE I. INTRODUCTION The automotive world is always bustling with enthusiasts and constantly developing in terms of performance and standards. Advancement in the automotive industry is also driven by a variety of sports competitions such as Formula, Rally, Moto GP, Motocross, and others. Formula car racing is a competition that is currently the pinnacle of the automotive world research. There are various classes of formula cars, one of which is student formula SAE a competition designed for students from all universities across the world. The formula student competition organized by the parent organization of the automotive world is the Society of Automotive Engineers (SAE) and must comply with the regulations [1].Engine is one of the most critical components in a vehicle. This component produces power that is then transmitted to the drivetrain system to spin the wheel. In racing competition, the performance generated by the engine must be maximized. However, the effort to maximize engine performance often clash with the rules of the competition. Therefore, various research and experiments are conducted in order to generate optimum engine performance while maintaining compliance with the current regulations.Although combustion in the cylinder is the factor that affects engine performance the most, the design of intake system and exhaust system piping has been wid...

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One of the rules of Student Formula SAE is air intake must have a restrictor located after the throttle body with 20 mm maximum diameter. It causes engine power and torque decreased. To increase engine performance, modify the bellmouth radius and venturi restrictor length are some of options. The authors analyzed the effect of them on power and torque produced by KTM 450 SX-F engine of Bimasakti UGM's 9th generation car (BM-9). The authors made 9 design variations then simulated by Ricardo Wave 2016.1 and Ansys Fluent 18.1 software. The result is, greater the bellmouth radius and venturi restrictor length produced higher value of peak power and peak torque.